Boy truly believes he had a twin and the twin died, but his family claims there was no twin?

Oh my God. I have no idea. First of all, you cant blame anyone for anything if you can't prove it. I mean, maybe the parents are lying for some reason. Maybe the boy is lying for attention. Or maybe he is not lying, he truely believes it. You can't go on without more information. You need a date for the car crush, he says he was four so search the papers for that year and see if he gets more date-specific. A human being doesnt just disappear like that. Where did he live back then? You could ask the neighbours, the local registry, kindergarden, find the birth catalogue for his birthday date, etc. Why does he think his parents hide it? Does he suspect a murder? The problem is that you are embarassed to ask these questions and I understand, but your sister might help? You said she knows the twins name, maybe she can get you more information. Oh, and until you find something, be very careful, you dont know a thing about him and yet he lives with your mother and sister. Something weird is going on with his family, thats for sure, his father apparently beats him...or maybe he suffers from some mental illness like schizophrenia but he is harmless, but you dont know that. Could he turn aggressive towards your family? Im just saying.