Couple of thoughts:
1) I think the person responsible is close (family, neighbor, someone who works in the house). This would be irrationally random otherwise. NG isn't a celebrity - even if her daughter is. She isn't wealthy in the manner that usual targets for ransom are and she doesn't live a lifestyle where she's neccessarily exposed (she's not followed by papparazi or the media). There is clearly some knowledge of the house and the fact that there is no subscription for the cameras. Any halfway intelligent person would know that even destroying a camera uploading to the cloud will show everything up to the destruction of the camera - so I think destroying the camera was to avoid anyone watching live (NG? AG?)
2) The perp has a normal M-F 9-5 job. Saturday night / early Sunday seems to fit this AND 2nd note comes out Friday afternoon. Something tells me, based on the timeline - the perp has someone at home expecting them. The times loosely fit a night out: I tell my spouse I'm headed out with the boys. Bars close at 2am. Plausable to say we were kicked out at 2:15am. This would be a valid arrival home closer to 3am if I claim I'm going to a bar across town, stopped for gas, cigarettes, whatever.
3) Blood spatter on porch (as many have pointed out) appears to be aspirated at the doorstep and drops thereafter. The doorstep looks like a small step down or, at least, a threshold to step over - with NG's limited mobility, this step over/down might cause her respiratory exertion resulting in either coughing or heavy exhale through her nose. I think it was a nose bleed - the drops are round and mouth bleeds just don't seem like they fall that way. It looks like she was walking slow on the porch, the drops are close together.
4) I also believe the ransom notes are a distraction or a layer added to cover the real intent. I won't go so far as to say she's no longer alive. But something about the family theory seems to check the boxes. Let's say, hypothethically, you have three children. One is a TV personality on national TV, one is a poet married to a school teacher, and one is a retired Air Force pilot. Would one of them be in a position to feel not as financially secure or not as happy with their lot in life as compared to their siblings? Hypothetically, let's say someone at 10pm calls their spouse letting them know they just dropped off their mom at home safely - but now is headed to the bar in downtown Tucson to meet up with friends - after all, it's saturday night. Same person grabs a few drinks and then heads to NG house. They know the cameras aren't saving any recordings, but disconnects the doorbell cam because it would alert NG or even AG when the doorbell is rung or perhaps it can be turned on remotely by NG is she hears forced entry. Entry is made. No signs of a real struggle because you are known to the NG - until you assault her or she falls. You help her to your car (or a car). You may or may not have a 2nd person helping you - but you do have a place you keep her (is it a storage unit? a partner's place?) Either way, you realize quickly you ARE the prime suspect. You cannot leave your own house now without scrutiny or surviellence by police. You cannot provide proof of life because you simply cannot go to where you are holding her without being found out by LE. Your motive was money - maybe you did intend to kill her and sobered up and realized that was stupid. Maybe the ransom idea then becomes what you go with - which explains waiting so long to send a ransom note. The family records a message on Instagram because they know you'll watch that. References are made to Silence of the Lambs - perhaps because they know it's probably you and that's meaningful to you. You see your wife struggle because you were "out" that night and arrived oddly late. Your brother in law also suspects you and his demeanor is flat because he's talking to you and you know it. You sister in law is full of emotion because she lives in NYC and isn't part of the everyday of the family dynamics in AZ. LE knows it's you and that's why they really haven't done extensive searches with cadaver dogs, sought that TX equestrian group, or had volunteers walking the desert.
With all that said - it could also be someone close to the family following the same script. I just don't believe the excess stuff LE is doing is really progressing the case. I think it might be to gather evidence to make the case stronger - but I think they already know who did it and they are either waiting for him to go to her OR they are negotiating with him in the background while maintaining "no suspect" for the public.
