I know every investigation is different but I'm getting a feeling that those closest to Lucas is NOT responsible for his disappearance. Here's my reasoning. Lets take a look at the last child who was last seen in their bed, Mariah Woods. At first LE treated it as a possible abduction but within a couple of days it became clear that she wasn't kidnapped. While LE never said anything official their actions spoke volumnes, particularly their search warrants for the home Mariah disappeared from, they seemed to be focusing a lot of energy on the house. Within a couple of days of the search warrant they had arrested the boyfriend for concealment of a body and they had Mariah within 24 hours.
Now lets look at Lucas. It's been 4 days since he was reported missing. LE has given no indication there was something fishy going on in the house, there have been no search warrants at either the current or previous home, there haven't been any so called "midnight interrogations" of step-mom or dad. There hasn't even been any legitimate evidence to indicate possible abuse save for the accusations on social media and some family members.
Oh...and something to say about RSO's in the area. I know some folks like to automatically go to RSO's in an area but keep in mind, every one knows who they are, they aren't quite as likely to reoffend since people are aware of their presence and LE keeps a tight leash on them. It's not the RSO's I concern myself with, it's the sex offenders we don't know about that concern me. They can operate with impunity and under the radar because no one knows about them.
All of this is just my opinion, I have nothing but past experience as a source of reference.