that's an amazing horror story. All the players, including the new girl friend's mom, and the kids. Incredibly complex and sad. And the big player, Death. Death of the girl friend's husband. It sounds like Bambi Meets Godzilla.
You gave excellent counseling to them at a time when you are down yourself. You have achieved many "points", good for you. You said that after they get counseling and it's still "go" for their love, then "go"! Because love matters so much, you were right.

Prayers for healing for all of you.