I wish I could help you.  That I could offer some sage advice.  I have been where you are now, and I can tell you that your role in this relationship will not bring you happiness in the end.  You are taking responsibility for two humans who, NO MATTER HOW MUCH YOU ACT LIKE THEIR MOTHER AND LOVE THEM LIKE YOU ARE, will NEVER be your children.  Dont read this comment to biodad.  He wont like it.  He will think it is harsh and unloving, but I can guarantee you that I know you are a loving person or you wouldn't be in the situation you are in right now, and it will only get worse.  You will soon be the one interacting with the schools, the teachers will think that you are the mother.  The kids may start to call you Mom, if they don't already.  You will sacrifice your career, your financial freedom, your goals, your alone time, your friends, and so much more for these little humans, and always in the way that your spouse tells you you should.  You will start to make every life decison based on the custody battle, and wonder how it is that when you leave the courthouse you are angry or sad, and she is skipping along with her SO.  I am going to repeat the meanest words ever told to me (by every single member of her and his family)  YOU ARE NOT THEIR MOTHER.  Now, if you want to become someones mother whom you can truly save, you can adopt orphans from a third world country, you can adopt a pet, and you can adopt a homeless person, but I can guarantee you that the path of taking responsibility for your Darling Spouses kids and Biomoms kids, will only lead to alienation of you from  the kids, and your own suffering.  I doubt you are going to listen, because I can't for the life of me figure out what I couldve said to myself seven years ago that would have changed my thinking.  I took them to the doctor, I stayed home with them when they were ill.  I rocked them to sleep when they had ear infections, I took them to all doctor appointments.  I refilled their prescriptions, and I spent every single day and night with them while BD and BM worked, hung out with friends, and did whatever they plieased.  Now, I know you are going to have a million excuses for your having to take responsibility for their kids, and NOT your SO doing it, but I am going to tell you as lovingly as I can, that there is NO excuse.  You want a day to yourself, and pretty soon your SO is working weekends, and needs "overtime" or to help a friend.  You want to put the kids in daycare, well, that would look bad in court, so you don't get to go anywhere.  Dad starts just leaving them with you without asking, and he does it regularly, BM does the same in the form of "I can't make it, My Alternator is bad again."  It goes on and on until you wake up seven years later and say "ENOUGH."  THen you fight until you get divorced because your spouse doesn't want a partner, he wanted a babysitter with benefits.  A real partner, knows that you need your own life.  That his responsibilities are his own, and that you can't fix his life.  He has to do that.  Dont be the babysitter, be the hero of  your own story, and start worrying about you first, and then put the responsibility on Dads and Moms shoulders.