In my view, it is best not to interfere in the R with H and his kids. Take yourself out of the equation for the moment as H needs to learn how to relate with D6 that involves the attendant emotions she has in regard to the trust issue.
However, you can guide and support D6 by allowing her to take ownership of her feelings and ask her if she would feel better if you were to approach H and say, "H, D6 has something she would like to say to you." Then you can move to another room so D6 knows you are nearby for emotional security.
Otherwise, H will think that you've been filling D6's head and feeding into her insecurities. Then he'll target his annoyance and anger to you for "setting" up H. Tread carefully, dear Busting.
I do get what you're aiming for in rebuilding the family. You can honor this by allowing the relationship to flourish between H and D6 by stepping away from their convo.
