Opinions please...

Long post...sorry. We did things a little backwards. We met bio GPs through a family member about a year and half ago. At the time, bio GPs had placement of their grandchildren for almost 3 years (ages 3 & 5 yrs) and were seeking a forever home as bio parents weren't working the plan or seeking the help they needed to get kids back. They wanted someone to take them that would allow bioGP to still have contact with the children. We met the kids, spoke to their worker, and became foster/adoptive certified. We agreed to openness and continued contact from the start, unfortunately, we didn't take into account that we really didn't know these people very well. Six months into visitations/getting to know the kids, bio GPs start doing some questionable things like telling BigBoy he isn't moving, having him call them mom & dad, allowing visits with bio parents against court orders, and very emotional outbursts from GM. Of course this confuses BigBoy and starts the ball rolling on some major emotional issues for him. LittleGuy is still young and doesn't really understand so he doesn't have too many issues, yet. At the beginning of this year, TPR for parents was granted and we took placement of both BigBoy and LittleGuy. Since then, bioGPs have been calling almost daily, and have had monthly overnight visits, which always end with GM crying and upset, not wanting to let them go and causing the kids to become upset. When we reached out for help from the worker, GM became enraged that the issues are "on record" and threatened harm to herself. We cut back contact to 1 call per week and future visits to be every other month, but GM already tried to change that. We are now into the adoption stage and will be finalized within 3 months (Yay!) Our new worker brought to light some issues we were not aware of at the beginning when we agreed to openness. We thought bio GPs volunteered to give up the kids but found it was never an option for GP to keep the kids permanently due to "issues in the home." With this information and all the issues we have had in the last year and half, we wonder if we should continue contact with bio family at all? We read about how good open adoption is for the kids, but what if it is doing more harm than good? GM already accuses us of "stealing" the kids. We also worry that visitation might be a safety issue as we were advised by the worker to have daytime only visits where we can supervise contacts. Should we just cut ties and get BigBoy into therapy for the loss? The worker says it is up to us, if we want to stop contact he will help. Is it possible for the relationship to heal and the future be better even if GM denies she needs any help or therapy? I don't ever foresee a friendship with the bio GPs but we want to do the right thing for our kids, even if we are uncomfortable. Has anyone else had a bio family member that just won't let go and won't let the kids move on? How did you deal? Opinions would be great. Thank you!