P.G.
I think it is so beautiful that all the adults in this situation want to do what's best for the children. To have a blended family like that is just so rich, and so giving of you all.
I think perhaps talking to a family therapist that deals with blended families would be a huge benefit. There are a lot of emotions that are going to come up for ALL of you, so get some help to make the transition as smooth as possible. There's going to be more of you all to love :)