Chad, Lori and Alex are the sort of lazy psycho that would ask you to walk to your grave site and dig it. I'd expect that having to move a dead body and the extra work would have annoyed them, so they wouldn't.
Chad is simply too lazy to have not done this in a way that would put the least strain on him so he could move onto something he wanted to do. I've been quite convinced the children were buried somewhere he was familiar and comfortable with. (could have been wrong, it was just my take on this man) Looks like that's exactly what he did. It was possible that he might have picked a graveyard he was familiar with, but his own yard certainly fits. How anyone looks at Lori and imagines she'd risk breaking a nail is surprising.
Yellowstone involves work. Most people do not go into any area more than 1.5miles. Lori doesn't seem to be the going for a nice hike type and clearly kept Tylee in a way where the kid didn't get to go do things much. Alex also doesn't fit the profile of someone who would do the extra work to walk in. Now though, Chad's little prepper cult buddies could entirely have stuff about how to dispose of bodies so it is possible he would have known about doing so, but being lazy it doesn't seem likely he'd go to that level of work.
I think Tammy was first and that Chad watched her die. That Tammy knew he was screwing around and between that and Lori having killed her husband he needed to bring his level of commitment to the moment up. Being challenged in his authourity and having Lori on his *advertiser censored* would have been a toxic combination for a malignant narc. He had to buy in or cut bait. Tammy knowing beyond any doubt of his betrayal would make being seen as a champ by her now too hard, but Lori thinks he is a hero of the ages. A general of the apocalypse. Uncovering a narc is super dangerous.
My guess is that Chad killed both kids, but Lori is the one who set it all up. Now there is the possibility that Lori murdered Tylee. If Tylee had done anything to threaten Lori or seemed like she was taking any steps to defend herself or JJ, with this new idea that Tylee was a zombie, so dehumanized, all the rage Lori has could certainly account for a more egregious attack on Tylee. I can see it. Basically Chad is likely a fastidious little **** and had no reason to be vicious with Tylee. Lori however - Tylee was more mature than Lori, loved JJ, she was everything that Lori isn't. Maybe Lori went after Tylee, and Tylee defended herself. No one but Lori has a reason to be a vicious petty villain to Tylee. Lori would enjoy being vicious, or at least watching someone else be so. Tylee had challenged her authourity by growing up and not being a sociopath.
Now it could be that Lori killed her then demanded that Chad follow through on his rituals of sealing zombies. Which may account for some of the egregious treatment of her remains.
Feeling sorry for Chad maybe being under the spell of Lori? Think Tammy just died naturally?
Chad knew a kid was already murdered and didn't move to save the other. Even if you think he just got himself in to something, he could have saved the other kid. And didn't so he could go screw blondy in Hawaii. Man isn't a sock puppet but a fully willing participant.
