lots of love.... lots of patience
when you and dad have youngest child, show love, lots of it, try not to argue points made by mom, just reiterate that dad and you love her and your her friend and yes she does belong to mommy, AND DADDY, we get that one a lot....
we also get a lot of this is not my house, mommy's house is my house, after couple months of gentle reminders son now says i have 2 houses, he has his own space and is allowed to be his own person
we have pictures of his mom & her family in his room so that he knows we share, its hard, it hurts, you can only fight back with love and patience and constant gentle reminders...
may you have a peaceful holiday