Need help dealing with stepchildren and ex wife?

My boyfriend and I have been together for 3 years and have bought a house together. He has 2 children 20 and 15 and I have 3 teenage children. All the kids get along fine. His children go months long without speaking to him. His daughter (20) only calls when she needs money and she LIES all the time.

His son calls when he needs something or to brag about something he got. His ex-wife tells his kids to call their dad because she can not afford shoes, cell phones and such even though she makes more then my boyfriend. The son that lives at home with the ex-wife always has new stuff but is always saying his mom can't afford anything. The problem lays I think with my boyfriend and his ex-wife.

They have spoken words to eachother MAYBE 5 times in 3 years. No communication is leaving it for the kids to play them. My boyfriend had been married 20+ years but had moved out 4 or 5 seperate times. His ex-wife and him never did anything together and always fought (per the children).

This time when he moved out he didn't go back, then we met, so she blames me for the divorce, She even goes as far as not take her son out of the school my kids go to so they don't have to see eachother all the time (but they get along great). How do I handle this situation. I do not think we can go forward in our relationship with all the straing from his ex still on us.

Source:Yahoo Answers