Spoiler I solved that problem by killing his wife and brother first.
Yep, that pretty much settled everything for me
I tried my first multiplayer session last night... had a blast. Pretty much as soon as I joined, I got invited to a posse, which I followed around as they did gang hideouts. After a couple of hours, a couple of our members start betraying us... this just lead to the complete destruction of the entire posse. Those two turned, so three of our members went after them and the other three of us just got picked apart by this other posse.
I went lone wolf after that. Stayed away from the more aggressive players, stood my ground when I had to, and didn't get ganked too much.
Just wish other players wouldn't kill you on sight all the time.