D..
You need to go talk to your pastor about this. It's GOOD that this is about about the church and a mentoring situation, because you can do something about it by talking to the minister.
The minister needs to have a meeting with the mentors and tell them that they have fallen down on the job. A mentor's job is NOT to sabotage a marriage by coming in between a husband and wife. And that is essentially what they have done.
If he is a good pastor, he will tell them that they are not to tell the husband WHY they aren't inviting him as much. They should curtail the time they spend with him.
Once this is done and they aren't calling him all the time (which I really hope is the outcome of the pastor's talk), ask your husband to go with you to the pastor for counseling. The pastor does not have to talk about his prior knowledge regarding this couple. You need to talk about wishing that your husband were more connected to the family. In the discussion, you can mention him going out with the other church couple over your kids' recitals and ballgames, and the pastor can tell him that this is not what a father is supposed to do.
Try this, Lilly.
Good luck,
Dawn