It sounds from what you have described as though the mother of the cousins should take more responsibility for the actions of her children, especially the older ones. If they are beating each other up, maybe it's not a good idea for them to all go on holiday together.
No not always. When at home he doesn't pay any attention to the little kids & usually sticks with the 15 year old cousin as he idolises him however he does usually argue a lot with the 13 year old as he is quiet argumentative, hyped & aggressive so they seem to feed off each others energy.
