step-mom considering adoption, want adoptees perspective

hope some one there can help me with some very painful issues I'm dealing with with my step-children. I am wondering if an informal adoption might help. Please read my story, questions are at the end. Here is our story. I am 58 years old and have been married for 21 years. When I married my husband he was the custodial parent of three children from his first marriage. The children were Avi, then 17, Rivky 13, and Moti almost 10. I have really gotten scant history from my husband, and from friends in the community but this is the background as I understand it. When the youngest was about 1 and a half, their mother suffered post-partum depression with some psychosis and was diagnosed as schiz. She was in and out of the home and in and out of the mental hospital. The children were apparently in and out of foster care and children's homes. The children were also apparently harshly treated and again perhaps actually abused by their parents. Their father divorced their mother when the youngest was 5, that means Rivky would have been 9 and Avi about 11. This was in early 1982. I came on the scene in 1987, but there had been a brief marriage somewhere in between. I knew I would be raising his children in a first marriage for me, and I had aat that time no children of my own. My husband asked me to treat his children as I would my own children, which i readily agreed to as the only thing that made sense. At the time of my marriage, my husband talked about his children as orphans, not only to me but in their hearing. They had brief supervised visitation with their mother who continued to be under psychiatric care. Then unfortunately in 1990 just a few days after the birth of my second child (a half-sister to them), their mother died, leaving them "motherless" at the ages of 20, 16 and 12. Most of the years of my marriage were incredibly difficult times between my husband and I, we often argued. loudly and in front of the children. He gave over the message at these times that I was an intruder, that there was only me "against four" of them, and that if I was unhappy with anything, I could just leave. After about 7 years of marriage he was finally able to say that he loved me and also loved his children. Since then things have improved in our relationship, but it has been in fits and starts. About 6-7 years ago I was actively seeking divorce. (By then all my step-children were married and forming families of their own. From the time I married, these children have been in my care, or once they married and lived out on their own, it is to our house that they return for holidays, family events, and summer vacations. Some have even lived here with their spouses and children for months at a time when there was some kind of need. I am closely involved in their everyday lives, and all their children see me as the grandmother. I definitely consider myself as their step-mother and have tried to relate to them as I would /do my own children. That has been my approach from the beginning and thru out the 21 years that I have been part of the family. Yet, Rivky even now (at age 34), sees me only as her "father's wife". And literally cries that she "never had a mother." I have told her and shown her over and over again that I'm there for her. Yet I still get the same response. Moti is the same, he will get into a depressed state and crying jag and all he can say is he "never had a mother" I am very hurt by this because I feel "What have I been doing here for the past 21 years?" Since Moti was 10 I've been telling him that he is "my boy in my heart and it's up to [him] if he wants me to be [his] mother." I also feel that if someone was so desperate for a mother they would be happy to take what they can get whether it's a foster mother or step-mother. I am beginning to feel that they are just wallowing in self- pity. But before I call them on their pity-parties, I would like to know if their thoughts and feelings are to be expected and accepted, even after all this time. Recently I was reflecting on my own childhood family and the not so positive relationships I had, still have there. Then I realized what my birth family couldn't give me, G-d had stepped in to be a "Father" to me and had "adopted" me thru my conversion to Judaism. This train of thought led me to think maybe I should adopt my step-children. Yes , they are now grown adults, but maybe it would give them the sense of permanency and my commitment to being their mother. It would not be a legal adoption, but a symbolic one, I would make up some kind of certificate and do some kind of presentation of these certificates. Other than that sense of permanency, what benefits does a child receive in a step-mother adoption? Obviously they aren't going to get a name change or the kind of benefits that accrue in step-father adoptions. Thank you for reading this. I would really appreciate hearing from people about this. Ima2all