darkriver like Ted am not sure I can make a difference but I will have a go.
A birth parent is not nothing, you are the person who gave them life. You had the odds stacked hugely against you and you did as much as you could. I really feel from what you have said that that is true, I've read your posts many times.
But ultimately you have to live with where you are. One day these girls may well come looking for you, who will they find?
Will they find the woman who battled her own demons/bad past and came to a sense of peace? I sincerely hope they will find you at peace and living the best life you can.
I do not know what charity there is for people in your position.Maybe there is not one.
So I wonder if you can take some wisdom from other charities/organisations etc for help.
For example can you find ways to make a place to go and be at peace and think of your girls. Might it help to plant trees in a wood in cerebration of girls (in the way that people who have lost children may do)? I really hope this is not an insensitive comment.
Then go to that place and be there at special occasions?
Can you record your positive thoughts for the girls in a journal so that one day you may get to share this with them?
And record your negative thoughts (if appropriate) to share with your therapist when she is back in work.
I can't share too much here because it is not easy to do so but I've had a lot of problems with my birth child, who does live with me and dh and is now a teenager. (I normally talk about my younger child because he is the adopted one.)
I've had to accept many things that are difficult and my dd has been so unhappy. I've found that any little thing that can help her is what I need to pursue. We got her some pets to help her have some thing to care for, we let her decorate her room differently, change her appearance a lot etc etc. None of these things will deal with the underlying issue (depression, anxiety etc), but these small areas may help her in ways we do not know.
I think you may find some things help you better, whether that is to avoid situations etc or to find alternatives etc.
I do hope my suggestions are not offensive or upsetting and I do genuinely wish you all the very best to get through this tough time.