First, it's a great thing that you've made their adoption legal. You aren't on shaky footing here - you call all the shots.
Since you know them, you'd be best to decide if they would be a good influence or not. They could be introduced as an Aunt and Uncle, although the girl would most likely recognize her mother.
I wish you well. This is a tough call, but it's such a relief that you've made this legal and it's your call.
I totally agree with RockRose. You are legally these childrens parents and children need stability. I commend you for stepping in and becoming that stable loving parent in these children's lives.
You, as their parents, need to decide whether or not their biological parents would be a healthy part of their lives. Much of that of course depends on their current lifestyles, etc. I completely understand this is far more complicated given the fact that your daughter is their biological mother, but I guess what I would try to do is remove that emotion from the equation and think about whether or not you would be accepting of this if she were a stranger. This of course is easy for me to say not being in your situation.. I know this is your daughter, and my thoughts may be impossible.
It is a tough one. I admire what you have done but do not envy your situation. I wish you nothing but the absolute best.
I agree with the above. Are the children's biological parent/s together? Or are they living separately? How old was the mother when the children were "given up for adoption:? Have they found religion? Do they have other children? Would they make good parents? Is there any reason why you would not give them another chance, other than the legalities? It does sounds positive that they are together while making this this request.Another thing, how old are you and your husband? How many kids do you have? Do you have any understanding of making a really really bad mistake? Can you relate at all? If your child is "better", does she want to be part of your family? How important is it to get your daughter back into the fold? Did you give up on her and unwilling to let her back in ? With all these questions and probably a whole lot more asked and answered, The greatest may be this , Are you being selfish by not providing an access for these biological children to be reunited with their biological parents? People talk a lot about unconditional love, this is your daughter, if she has been rehabilitated are you comfortable as her mother to deny her her children. Do you believe in rehabilitation? Are you willing to take a chance on talking to her, because you may open yourself up to something that may result in a perfect reunion, that of mother and child., twice. You have a lot to think about i think. Please keep posting and reaching out!! Personally, I think you owe your child and your adopted children a meeting at least with a psychologist, not a lawyer.