Such sad stories here. I have a different experience but I am sure although my eldest sister (half) doesn't ever say so, she feels abandoned by my Mum. My mum fell pregnant out of wedlock at the age of 19, catholic parents. She was forced to go to a mother and babies home and the plan was to have my half sister adopted. She had a horrendous four day labour, and when my grandmother went to visit her, she decided that although she already had 7 of her own children, she would take my mum and half sister home (to the shame of the catholic community).
My mum and grandmother raised her in the house, then my mum met my dad when she was around six months old. Again my Mum thought she was pregnant, married my father within 3 months. My father promised my Mum he would take on my half sister as his own, but for whatever reason (jealousy I suppose) he didn't keep his promise. My mum felt trapped, my grandparents became the full time carers for my half sister. My parents went on to have 3 children. I thought my half sister was my Auntie until I was 10 even though they never hid it from me.
The situation shaped us all, my half sister and I are very close (as she is to my mum now too), but it was always the elephant in the room. I remember feeling gulity she didn't have the same as us, but actually she will say now she had a great upbringing with my grandparents and she was adored by all my aunts and uncles. We used to have holidays together all 4 of us, and I remember even as a kid feeling the tension. My father to all intents and purposes is a good one, but insanely jealous my mum had a realtionship before him. My mum always (of course) felt resentful andf guilty of the fact she couldn't care for her like she wanted too.
There is a lot of bitterness and resentment from both my parents, after 44 years of marraige they recently separated. My sister is an amazing person, although she holds a lot of anger, it is not projected onto the family, she just simmers a lot of the time. In hindsight if she had come to live with us her life would probably have been made miserable by my father. So i don't know if it was the right decision. My mum has regrets but then she says she never is regreful as she had 3 more kids she wouldn't have had.
My Mum, Dad and Sister have never had therapy, they all kind of ignore it and pretend its ok, but its had lasting scars on all of us. I know my Mum has made as sure has she can that my half sister (and all of us) are loved deeply. She is a good woman, just one who got caught up in a shit situation at the time. The late 60s early 70s were a different time from now I suppose.