I agree with your overall statement that that they all knew what was going on in each other's lives. She knows more than she's pretending to. However, I actually believe she has shown concern over LE's presence and actions, but she's desperately trying hard to pretend like it hasn't bothered her. And it is because of this that suggests to me that she is deeply involved and intertwined in this whole mess. Her words and actions betray a guilty conscience, despite protestations to the contrary. As an example, from the interview with Nate Eaton (BBM):
Eaton: When did you guys find out there was an investigation and JJ and Tylee were missing?
Melani: I’m foggy on this date but (Rexburg Police) Detective Hermosillo and another gentleman had come to my door while I was moving my stuff in so it had to have been early in November – I’d guess the second week in November.
I get a knock at the door, and I open it and see police, and I’m jumpy because what is my ex up to? What’s the next thing? Are my kids OK?
The detective said, “Do you know who lives next door?” And I said, “Yes, I think Alex’s name was on the lease, so sometimes my uncle’s over there, sometimes my aunt goes over there,” and I didn’t know what that was about. That was it. That was my first encounter with Rexburg Police.
Eaton: And that’s when they said the kids are missing?
Melani: No, no. This was early November. Then right before Thanksgiving, we’re driving down to Arizona to meet Ian’s family and have Thanksgiving, and I get a text from (Rexburg Police) Lt. Ball that says, “Somebody’s broken into your home. I need you to call me right away.”
I’m immediately like, “Oh great. My ex has sent somebody. I knew he had a private investigator following me, and I immediately thought he sent somebody to come break into my house. I didn’t know what to text back – I was kind of processing it.”
Then later, I texted back, “Well, I’m with people I love on Thanksgiving, and at least that’s what’s important.” If whatever the heck was taken – I had my emergency cash savings and I had a computer, an iPad, an old phone I didn’t use – I didn’t know what had been taken, but I was like, if my whole apartment is robbed, it’s OK. I got everything I need. It’s not about things.
Then he said, “I need you to call me,” and then I later found out it was the Rexburg Police. They had knocked down my door and taken a lot of my things. I kind of felt bothered about the text I got but I understand they’re just doing investigation.
As soon as I returned after Thanksgiving, I went right into Detective Hermosillo and was like, “What’s going on? I’m here to get my stuff.” He asked me about my previous marriage, what was I doing here, and he asked me about Lori and Alex. I was an open book and said, “Here’s what I know. Lori and Chad had left probably right around when I was going down to Arizona. They packed up and left, and I think it was a planned move. It wasn’t last minute because they had talked about moving to Hawaii at some point. They told Ian when they met, ‘You’ll have to come visit us in Hawaii sometime.'”
So here we have Melani admitting that she was nervous and "jumpy" when she first encountered Rexburg Police when they came knocking on her door. What would cause her to be nervous and jumpy around police? Well, the very next words out of her mouth indicate that it's because she feels it's in regards to her husband, Brandon Boudreaux. She couches her words to make it sound like it's because she thought Brandon was up to no good, or that her children were in danger, but I'm not buying it. We have the text exchange between BB and MP wherein she essentially tells BB that she was moving to Idaho and for him to keep the kids. He tried to get her to reconsider, saying that the children needed stability and their mother in their lives (this despite the attempt on his life, clearly he was concerned for the best interest of the children), but apparently she wasn't interested in that. He then applied for full custody and she never showed up to court to contest it. This tells me that she was trying to distance herself from him and the kids, for some reason. The only believable reason, to me at least, why she would be nervous and jumpy with the police knocking on her door, and why BB was the first thing on her mind, was because there had been an attempt made on his life just weeks earlier and in all likelihood she thought they were there in regards to that. And why would she be scared for that unless there was reason to believe she was somehow connected to or involved with that attempted murder?
Well, as it turned out the police weren't there for her directly, they were inquiring about her neighbor, and if she knew who lived there. She told them her uncle Alex lived there, and they left. One has to wonder if the police even knew Melani lived there and knew of her relationship with Alex when they knocked on her door that day, or if they were trying to covertly investigate Alex at that point. Anyways, Melani claims to have not known "what that was about," but I suspect she did. Why would the police be looking to find out who lived next door unless the person who lived there was a person of interest in some kind of crime or investigation? And it's obviously not in regards to the missing children, as Melani admits.
Surely she would have talked with Alex and the others about the police asking around about him, right? That probably would have made everyone a bit nervous and edgy.
Later that month there is a welfare check for the kids (initially just JJ, until later they discover Tylee is missing too) and everybody in this family scatters like roaches when a light switch is flipped on. Chad and Lori hurriedly fly to Hawaii on a "pre-planned" trip. Alex apparently goes to Arizona to propose to ZP for a quickie marriage... changing his last name to that of his new wife, against all conventions and traditional norms (one has to wonder why. Surely it has nothing to do with trying to evade the law and justice, right?). And then we have Melani, who also travels down to Arizona to be with Ian's family for Thanksgiving and have a quickie wedding and adopt a new last name. Something happened that made everyone up and leave town at the drop of a hat. I'm betting there was a hurried family powow in regards to the missing kids and/or LE closing in on them about the attempted murder of BB. Whatever the case, the entire family is conveniently gone by the next day when the raid is performed.
As Melani is conveniently on her way down to Arizona LE from Rexburg texts her with disturbing news about a break-in to her home and that it's urgent that she call them. And of course she doesn't. According to her, "I didn’t know what to text back – I was kind of processing it." I believe that. I don't believe her excuse that she thought it was BB's doing, otherwise she would have called immediately as the law would have been on her side. If it were a break-in and it was as urgent as the officer made it sound (and she should have had no reason to believe otherwise, unless she were a guilty party to something more nefarious) then she should have reached out immediately to the police by calling them as instructed. What if the police were trying to find out if she or other family were ok or had been abducted? What if they needed her help to find a potential suspect? What if they needed other vital investigative information? In spite of the urgent and serious nature of the text she doesn't act how one would think. She doesn't act normal (and it is an act that she's putting on). Instead, she seems to fear/suspect the police and so she takes time to "process" the situation before replying some time later with a text that was designed to appear at once both innocent and dismissive. Her text comes across as passive aggressive - oh, you don't need to concern yourselves over me, I'm with those I love and so you should stop ruining my Thanksgiving holiday over some silly little break-in. She then goes on to rationalize rational lies her attitude and behavior for not treating the communication with LE more seriously by explaining that she just wasn't worried about property that may have been stolen. That's not the point! LE needed to talk to you over the phone about an important matter and you are acting completely out of character for an innocent victim! They needed information from you, and you knew it, but instead of helping them do their jobs you showed that you were more interested in protecting yourself by actively impeding their investigation.
The detective then replies back, again simply urging her to call them immediately. Which she never does. Instead she ignores the situation completely for several days. It isn't until some time after Thanksgiving, after she has gotten married, and has to go home and face reality again, that she finally gets in touch with LE about the situation. After she has had time to "process" the situation and come up with a defense. And then she again feigns innocence and ignorance - what's going on? Where's my stuff?
I'm sorry, but her words and actions don't speak to me of an innocent person with nothing to hide. Rather, they only make sense to me in light of someone involved in criminal mischief (whether of her own doing, or those she closely associates with and supports) and fear of subsequently getting caught. JMO.
I also wonder, was Tylee's Jeep impounded by then? Last I knew, we didn't have the specific date LE located Tylee's Jeep and took it in to be processed, we only know that happened in Nov. Did AxC and Melani possibly take the 2020 Telluride to Utah because they couldn't take the Jeep? And how did Melani know that BB and their kids were in Utah at his parent's house on Nov 12th? Was there a mole feeding her info? Did she hire her own PI? Or could the police have tipped her off about the PI tracking her there when they impounded Tylee's Jeep with a warrant? And if the Jeep was already impounded and she knew that, where did she think Tylee was the 2nd week of Nov? 
, and an immediate scroll and roll (no offense). I just want her to stfu already.
