You should invite them to a restaurant or something, on you, and you let them know you want to hear what THEY have to say...

Try to focus on the facts, NOT on he said she saids... stay AWAY from that...

Fact : We haven't even explored family therapy yet
Fact : I made a commitment to love your daughter better or worse and I am doing that
Fact : There is a MARRIED MAN threatening our home and your daughter... I am not going to SIT there and let him turn our home upside down like some highschool bully.. I am trying to protect your daughter from this creep

Stuff like that.. it does NOT attack their daughter at all.. see?

It's hard to argue when you put things the way a parent wants to hear them.