AITAH for uncontrollably laughing at my sister's face when she asked me why her children chose to live with their dad?

“My sister Sofia(fake name)(42F) has some issues” is an understatement. I(28M) am a super surprise kid for my parents and my sister was at high school at that time so we never had a sister-brother bond. We are from a small town in Switzerland and sister has gone to study law in Berlin.

It was a culture shock for her. We are not prudish or conservative in the sense of politics and morals but we are not the most open people either. She didn’t take that well and at the 2nd year,she dropped out of the law school after a diagnosis of Major Depression and General Anxiety, came back to our town and got married to her high school sweetheart,whom we will call Gabriel. She went to a local vocational school,got her degree on medical secretary and she started to work at the local hospital in the town. She had her kids,the twins whom we will call Leon and Luca(15M). Her anxiety and psychotic thoughts have skyrocketed after the birth.

I was never allowed near her children after I was 16 years old because I might be a “groomer” since I want to go to Heidelberg to study medicine,she didn’t allow anyone but her MIL to babysit because we were always traveling to “corrupt places” (my parents and I travelled the world) and I was listening “Techno Music”. Gabriel and my parents have tried to convince him to go see a psychiatrist but she vehemently refused other than anyone who is the pastor of our towns church (to be fair, pastor’s wife is a nurse in the local hospital and he was also saying the same things with us). Until the twins were 8 years old,this continued. They weren’t allowed to leave the house unless Anna,Gabriel or MIL was with them. Me and my parents weren’t allowed to come near to them unless they were supervised by Anna.

When they were 8, Gabriel had enough and he filed for divorce. Swiss courts are not known for their swift decision making capabilities but to strengthen his hand,me,my parents,MIL,the town’s pastor,his wife and the kids teachers have all given statements. Due to the count of statements, clerk has pushed the process and full custody was given to their father after only one court session. At that time I was in medical school.

After I have graduated from the Medical School,I came back and I have decided to continue my residency in Switzerland. I currently work in Zürich and my hometown is just a 75 minute train ride so I usually spend my golden weekends or long holidays in the town. Last week,I had a one week off and I went to see my parents. My sister was there to our surprise,she was crying hysterically after the kids have refused to stay with her after all she did(She goes to therapy,she was in an inpatient ward for a month after the divorce due to a catastrophic breakdown which includes serious self harm,she is currently on 3 different medications etc.). Their relationship has improved but at 15,they were asked again for their opinion on custody situation. They said they didn’t want it to change and they don’t feel safe unless they were in public with their mother or some other person were present.

I have listened her rants for a hour until she asked me “Haven’t I suffered enough,why they don’t choose to stay with me? What can I do more?” . I saw her face,she was dead serious and I have started to laugh,not as a pity laugh but I have lost it at that point. I have laughed for a minute while she was looking at me with a blank stare and I said “You seriously think they will trust you again,I am sorry but you have to let it go. If you were my mother,I would have wanted to get a restraining order against you. They are much more gracious than I am.” and I have left the house to see my nephews.3 hours after that,I have got a call from my parents that telling they were at the hospital after she tried to overdose herself with my mother’s hypertension medication. She is freshly out of ICU and everyone other than Gabriel are.blaming me for the situation. AITAH?