Hello and thank you for your question.
Do you know exactly what your brother in law said or did to your son? Also, is the first time he has been scared of your brother in law or have there been other incidents as well? I'm asking this because your son's reaction was quite severe with not being able to sleep etc and never wanting to see them again. So, I'm thinking maybe this either was not the first time or it was quite serious what did happen. Do you know the details and what does the Uncle and his wife say to you about what happened. Thank you for the additional info...
Okay thank you for the additional information.
I think that it would have been okay for the Uncle to simply have asked your son nicely to turn off the game, as the little girl might hear it or see it. I'm sure your son would have obliged that request. So, the Uncle did not need to talk to him in a stern tone and say insulting type things to him, etc. as I'm sure like you said, your son was trying to play his game responsibly. If you were also at home at that time, then the Uncle could have come to you first and that would have been better. If you weren't there, then he could have (as I mentioned) asked your son in a nice and respectful way to perhaps turn off the game or play another one.
I don't know if this is worth however, never seeing these relatives again, as it sounds like the kids might like being around one another and this isn't a regular occurrence. I would ask the Uncle to not speak to your kids in an aggressive way or discipline them, that is your role. And that if there is an issue in the future, to discuss it with you first and that you will handle the discipline of your own children. Please click ACCEPT button for this answer. Feel free to continue the discussion, even after clicking accept. Thank you.
I would probably let some time pass then, without having this conversation on the phone. It's not like they are going to be around your kids soon, as they are not in the same town. Or, you could also email and say, I just want to move past what happened, and put it behind us. I would ask however that Uncle simply just let me know if there is an issue with the kids, and I will handle it as I see appropriate towards my own kids.
And then let it go.... and hopefully it won't happen again. You could privately tell the uncle or your sister that your kids are not used to that kind of tone, and it scared them. so to just leave any issue that is about your kids, for you to manage. That's it!
You don't need to cry about this or get all stressed out. just communicate simply and firmly. email is good for this and then be done with it and move forward. all the best!