I agree with Gardener, Hmama. Take it slow with the letter. Mull it over. I don't see anything, however, wrong with contacting those you were close to, i.e. sisters-in-law, etc.
My brother-in-law is in a similar situation. He has no family there (he lives very far away from any of us). So, as the process of the D continues, he tries to keep things calm. If he is invited to family events, he goes. Fortunately, his D has proceeded very well, as much as a D can. Lots of mediation, children in counselling, etc. It was his W who left, but there doesn't appear to be an OM. I think the loss of extended family is a common thing. It probably hits the kids too. But, he and my H are victims of D, so I guess they have experience.
Me:57 H:52 M:28 Got another lawyer last year and filed. D35,S/D twins28,D22 EA4/04 End? Who knows? "Life is like a mirror. Smile at it and it smiles back at you." — Peace Pilgrim