Too many possibilities. If all three missing are deceased, it could be that:
1. There are actually three bodies in that car but the fire was so intense that police have only "found" 2. (Less likely)
2. One of the trio was lured away and killed on the spot or murdered elsewhere. The second POI could've come to the car from another direction where there are no security cameras. This second POI could be someone the three year old and this trio encountered at another point during their stay. (Don't find this likely either)
3. One of the three double-crossed the other two and was in turn double-crossed by whoever helped murder the other two. (Definitely more possible than the other two previous options)
Still seems most likely that one of the missing are still alive. Drugs clearly seem to be involved with this. But it's hard seeing how any of the three felt it worth murdering the other two over the profits from a kilo brick (or few bricks) of cocaine. Looking around, seems the cost of those are around $25k a brick/kilo. Why would any of them feel it worth living their life on the run for at most, idk, $200k? They'd have to be willing to throw everything and everyone they've known away to start a new identity elsewhere. One of these three would have at least a sociopathic level of ambivalence to the lives of the other two, if not outright contempt, anger, or disgust. Maybe they had delusions of grandiosity or toughness, wanting to seem like a "big time" hardcore dealer (thinking back to the Cosmo Dinardo saga).
Either way, heartbreaking if one of the three betrayed the other two and left this poor child without parents in his life. Nobody wants to believe a parent would murder their spouse and close friend in front of their own child, and abandon them forever on a doorstep. Nor that a family friend would traumatize a child forever by having both of his parents killed, especially a family friend that has only recently came out as trans*.
Unfortunately, it seems that the happy public image of these three differed from their private lives, judging by their family's lack of awareness of this interstate drug-running business. And the fact that they would take a 3-year-old on an excursion as dangerous as this. SOMEONE close to these three would have to know if there's anything else more to the story, like a history of conflict between any of these three that would incite one to leave the other two dead. Or if any of the three have fantasies, impulses, or delusions that would lead them down this path. I hope police in Florida are closely investigating the connections these three share down there, same goes to NY police in the connections the family friend had in Webster, NY. Though I'd imagine interstate drug trafficking will probably bring out more agencies than local/state PDs regardless.
IMO, the dad is carrying too much body fat to be the POI that was running away with the three-year-old, judging by surveillance footage. And whoever did this is not as smart as they probably thought they were.