Talk to your son to find out why he wants to run away. As for his sister, well...nefarious people are gonna be who they are so it's only a matter of time before your daughter is a classic scammer.

She's not wrong, is she? The main problem that I see is once he runs away, she might take action to speed up getting that inheritance, if you know what I mean. ;)

It is pathetic when parents or grandparents try to control their relatives by using the promise or threat of an inheritance. Do you really want to seem more valuable dead than alive? In the end an inheritance usually doesn’t live up to the promise anyway by the time it arrives - If it arrives. Stop all talk of an inheritance - Talk instead of now and the near future which is all that usually matters to a young person. You are raising a monster of a daughter if she’s trying to manipulate her brother out of the picture. It may be a consequence of whatever message you have been sending about an inheritance or possessions. You need to talk to your son about why he’s unhappy - And listen more than you talk otherwise you won’t know the real issues. Some family problems can be fixed, most get better if both sides communicate.