only one side of the story

so the other day im talkin to my sister and the conversation is going good then all of a sudden she then leads to say that my grandparents do not care about her or my brother and that she felt it was wrong for my grandparents to kick my mom out when she was pregnant.....i was trying to get my sister to see that there were many reasons as to why my mother had to leave my grandparents house the way she did but she kept saying that her other grandmother and father told her something else which i already knew were lies and she didnt want to believe me.....so i told her some truths that completely dispelled what her father and grandmother were telling her and she kept saying w/e....but i was like the only ppl that know their child the most are the ppl who raise them not the ppl they hang with and if she wanted to know more than she should talk to my grandparents and then make HER OWN OPINION based off of what she hers b/c it is wrong to only hear one side of the story and make judgement.....i then talked to my grandparents about it and they said that they expected my sister to feel the way she does b/c the other side has completely brain washed her and my brother.....my family is so crazy....i just want for us to all come together and be the way we used to before my mother died