I have had a different experience with my H family. We have been in contact every few days since this whole thing started. My friends cautioned me about carrying on a relationship with them considering their allegiance is ultimately with their brother/son. But his family is concerned about him too..so we keep eachother posted. I am careful not to reveal too much to my H about my contact with his family..although he knows we are still close. (went to his sister's baby shower, went to the hospital when his sister's baby was born, been to lunch with his mom several times, still on all emails that are sent to the family).
I guess it really depends on what kind of relationship you had with them prior to this whole ordeal. My H family knows everything that is going on and provides me with nothing but support. This was the case from when I first found out about his A. If you were close with his mother..give her a call and ask to meet her somewhere. See if she brings anything up..and then go from there. You don't want to have R talk with his mother if she doesn't want to hear anything. (agree with citygirl) Wait for her to initiate.
My H family told my H that they would never accept the OW...they would respect the fact if he decided to end his marriage...but under no circumstances will the OW ever be allowed in their homes or lives. It made me feel good. They are ashamed that my H has behaved this way...usually to tears.