Hidden friendship between Mother and Mother in Law for 24 years

Hi, am I new here and need some advice please. After my mother's death, I discovered that she and my MiL had been friends for 24 years without me or my husband being aware. Apparently they met at the hospital when our first child was born. It was a traumatic birth and we nearly lost our daughter. Over 24 years, they had been to each other's houses and several events without us being aware even though we were involved with both women and even lived nearby to my MiL. My Mother, who left the family home when I was seven and didn't ask for custody, had used the friendship to basically paint me as 'vile, evil and insane' to my MiL. MiL's sister actually sent a text with those words when my husband expressed how hurt we were at finding this out. My Mother treated me and my siblings as though we had 'sell by' dates. I was troubled in my 20's and hospitalised 3 times for eating disorders - this was the basis of me being 'insane' and a 'drug addict' (I have never taken anything other that what has been prescribed for me). She was never supportive, used everything against you and even tried to break her children's' marriages, succeeding with my brother's. So many seemingly bizarre things that have been said and done over the years makes so much sense in light of this. The impact this had, feeling like our lives were in the 'Truman show' has been immense. I know this may seem trivial in itself, but, in the middle of all those years, we were told by our eldest child that she had been abused by my father. We told the police, went through an horrific Crown court case and have had to try and rebuild our family life. Our eldest daughter has since been diagnosed with BPD-we have sought out help but it is not served well in the UK. We looked at so many options but BPD suffers do not always recognise they have it - she is an adult and high functioning. She is also very much with her paternal Grandmother's opinion now, stating people can be friends with whomever they choose and she doesn't want contact with us which has been unbearable. I encouraged our daughter to be in contact with my MiL but am now aware that the connection has been used, to quite a large extent, to denigrate me and this has not helped her at all. I can just about cope with the horrid things MiL has said, but am deeply concerned that this is harming my child further- MiL does not 'recognise' mental health issues. I don't disagree with the friendship of the 'mothers' itself, it could have brought families together, I just think they should have said something. At the time of the trial, neither set of families were there to support. We now know that my Mother painted me as a liar, a thief and told my in laws that I probably put my child 'up to it'. The abuse of both our children (my youngest too, was harmed) shattered our world completely. We had fallen out with my MiL as she was constantly treating her other grandchildren better than our two (treating them to holidays/circus etc) and our girls would come home in tears, my husband confronted her and I was blamed, in fact, I got blamed for most things. I tried to reconcile the family and encouraged the children to have a bond with MiL - my eldest did but my youngest has never been keen. My husband felt I nagged him to build bridges with his family. I wish now I had listened. 3 years after a guilty verdict that saw my father imprisoned, my Mother in Law asked my eldest child 'if it was all true'!! My Father in Law was in the police and would have known how a trial works. The family is broken, our eldest child (who told my my MiL 'dehumanised' me), no longer has contact with us and I am aware my MiL has told her the things my Mother told her about me - mostly untrue but good gossip. I had tried to look for my Mother in the later years, I told my Mother in Law this too - my sister had breast cancer and was crying for a 'mother'. My sister's reaction when she realised our Mother had known she had cancer and made no attempt to reach out, was heartbreaking - my husband apologised for his Mother's deviousness. Am I being unreasonable to think this was such a horrible thing to do to your family?I tried so hard with my Mother in law. She was actually worried my husband would turn up at their home as she had been given my Mother's dining table and she thought he would recognise it and ask questions!! I kept saying to her how we could visit as a family but rent a nearby cottage but she kept making excuses and this hurt my husband so much. She is heavily involved with the local Church and told my daughter 'she forgives me'!! After my Mother's death, I found out from a cousin I had not seen in decades, that she had known my father had abused a child when he worked abroad and yet she left me and my siblings with him, whilst she enjoyed a luxurious life with my Step father (a known drunk). My father never harmed me or my sister but the knowledge my mother had, and never shared, was true and could have saved my children from the terrible harm he inflicted as he was the one person we felt was interested in being part of our family. My counsellor says my Mother had very prominent Narcissistic personality traits and that she had to put me down and demonise me to make her choices look better-I would literally do anything for my children, my youngest lives nearby and we see eachtother almost daily, we have a loving relationship. I would do anything to have my eldest back but have researched BPD and know that the strong emotions of reconciliation emotions could harm her and that worries me. Sorry for rambling. I know that I had a tense relationship with my MiL, I was never good enough - but I don't believe either my own family or I deserved this treatment.