That's where I'm leaning too. I suspect that Kenneth was the first target, though. He was probably particularly vulnerable to being robbed and/or double-crossed, being out there alone. Although there were other family right down the road who weren't targeted. I think there's an easy explanation for that. Maybe he caught someone else stealing? Someone he knew? Just an idea I have. Then that person or persons out of desperation killed him. Maybe the money that was allegedly strewn around him or his camper is a way to make it look like some cartel did it, or maybe it provided in the perp(s) mind a way to point away from the real killer(s): "Look, someone left money!" (i.e., "It wasn't me...otherwise I would have taken the money.") Maybe the money was brought by the killer, who gained entry by lying and saying he/they were returning the money that had previously been stolen. And the money, whoever it belonged to, may have been dropped by Kenneth while this person(s) was robbing him or after being confronted about stealing. The money couldn't safely be gathered up, then.
After Kenneth was robbed and killed (again, just speculation), since this is a person or persons known to Kenneth and therefore probably the rest of the Rhodens, the rest of them had to be killed because they would know right away who did it, especially if that person had been accused by Kenneth. Chris Sr. and Gary might also have been robbed or attempted to. The alleged beating/violence could have happened for any number of reasons: a struggle, trying to force them to reveal a hidden stash, open a safe, something like that.
Like many others, I think most members of the family were massacred because they would have been able to identify the killer(s). This would be especially important if he/they were known to them, and EVEN MORE SO if this person had been previously accused of stealing.
Again, JMO, subject to change.