Well it is, WM was not a member of the country club set. Every neighbour reported the family (WM & DM & MB) kept to themselves. WM, deep in his cups and with his dented up truck, sounds like a bit of a hillbilly. Not an opera-goer, anyway. WM is likely not the connection between DP and DM unless WM had a tricky impaired charge to deal with or something. They would not run into each other socially...especially if WM stayed home with a bottle and the blinds drawn most of the time.
It's DM that wants to rise above his hillbilly upbringing and live a life of wealth and privilege full of raves, clubs, coke, women, dining, travel, gifts, cars, etc. etc. He's been to private school where he could rub up against other wealthy people (and probably see how unsophisticated his father was compared to the families of his peers.)
I think one of DM's party buddies had DP as a lawyer. DP has defended rich kids drag racing, drug charges, etc., all the B.S. you can get into as a young man.
I don't think DP is a family friend (i.e., did not meet through the parent)