Extremely bratty 8 year old advice?

My husband's nephew is a right brat and whenever we see him he is rude and unsociable, never says please or thanks, swears and kicks up a fuss until he gets what he wants..he is totally spoilt by his parents who give and do whatever he wants as they are under the belief that ' children should get what they want as they are only young once'.If we go out together it's only doing things that he wants and I have had enough we have a little baby age 2 who he totally ignores and says that she is a pain when she wants to play with him..He has never once slept in his own bed.at 8 he still sleeps with his parents plays on the nintendo all day and is not difficult at school but is behind his peers: his parents say that the teachers are too strict and it's their fault..Other family members have frequently commented on the situation but have had their tongues bitten off by his mum: should I just bite my lip too? It's a shame as my brother-in -law is the sweetest kindest man you can imagine but is totally under the thumb of his domineering wife..Advice?