Going on holiday this summer again with DH's brother, SIL and 9 year old DS. Our DS1 is 2 years younger than him, and they have an interesting relationship. All the adults get on like a house on fire - we tried a holiday together last year, and it was fab, APART from the incessant winding up of DS1 by his cousin. It used to be very physical, (Cousin locked him in a suitcase AGE 1 and sat on it, wasn't even told off), lots of snidy things, and now ultra competitive, "I'm better than you" constant winding up. DS1 rises to it and gets v upset. we thought they might have grown out of it by this year - but had Cousin over to sleep last week and exactly the same happened. Ended up by 8.30pm with DS in tears, refusing to sleep in same room as cousin. Difficult for us to say anything to BIL and SIL. Now dreading holiday. Have DS2 who adores cousin. Any advice?