problem is the rest of the family (parents and siblings) just aren't on board with it. I don't think they've even read all the links I've sent them. They don't want to do the positive reinforcement stuff they don't believe in it.

man... this is an unfortunate and a difficult scenario. Your parents and siblings can easily reverse and even "poison" cues and commands. Is there any way to have them just not even attempt to train a dog at all for a week? Can you convince them you'll be the only one to work with the pup, they can play with it, take him out to potty, but that's it? And then you bust your ass doing positive reinforcement stuff? Maybe when they see progress, and they will, they'll change their minds? Otherwise, given the mix of breeds you're looking at, this can become very problematic....

Wtf do they believe in if they don't believe in positive reinforcement? Would they rather hit a dog than make him work and figure stuff out? I'm not an expert, and I'm sure there are scenarios where something more than positive reinforcement is required, but man... seems like your family is just not giving the dog a chance to succeed. It's sad.

They unfortunately don't leave you with much choice... try to take ownership of that dog and work as much as you can with him. It'll be tiring and difficult, but what's the alternative? Potentially neurotic large dog? Pass.