Ok.....luckily my son loves his older nephew....so that helps in our situation. I agree....a socialy acceptable rule is alway: no one hurt each other! Even your sisters difficult child needs to know this! I will be watching them and ask your sister to intervene if you see some one being rough!
I agree...a close friend can also help. What me and hubby do is to take turns to entertain difficult child.....maybe one will take him for a walk, or play ball outside or watch a bit of movie...Obviously the family dont understand this and think kiddo is just being spoiled and manipulative! Wont help even to try and explain it! If you dont live with a difficult child, especialy some one on the autism spectrum.....oh boy, you will never understand!
What also helped some times: Me and difficult child decided before the time on a non verbal signal, maybe showing thumb up, thumb half way down and showing down.....if he feels his tolerance is getting lower.....and then decides what plan of action will be taken.....This helped my son feel saver! In our case my son said if he starts to feel this way, I must just make some space for him to come and sit closely next to me.....or we can go for a walk.
Ok....the problem is if you go for a walk, sometimes he doesnt wants me to go back in....and then the pressure starts building upfrom the other family members.....I do understand that its difficult because even though my son thinks he loves rough play I can always see him getting more emotionaly upset and then he doesnt want to stop.....maybe then you can intervene and say ok.....time for ice cream or something salty, or whatever you know brings your difficult child down? Sometimes I will also intervene if the pressure is building up and say....ok I think its time to go and play outside and get some fresh air????
Will be thinking of you! This might be very stressfull, but just remember....this to will pass! And maybe even try a little bit of bribing if needed!