Hi trixxie!!
I agree... be Switzerland.
"I love you both very much and hope that you can work it out." Offer to watch the kids if they want to go to counseling. Other than that...
I will say though that whatever the issues are, your DS living in your house needs to be living there as an adult boarder and not as your son. I'd be tempted to do his laundry, cook his meals along with mine, etc. I think maybe he needs to be very clear about what life as a single dad would be like.
Good luck, to you and to your son and DDIL.
