DPs cousin died last year and left behind a newborn baby so the family all chip in with his care, but mostly his nana and grandad care for him. The family's very close and so obviously when our baby is born the babies will be very very close too, he often even stays over our house. The only thing is, they're REALLY over protective of him (understandably) which has lead to DP also being very over protective and so the little lad is now quite spoilt- eg today they've just bought him his THIRD buggy (£200- he's 15 months old) because he doesn't like the other two. He's also taken to screaming to get what he wants. He stays up all night every night, still has feeds through the night, and often refuses to sleep in his cot, so sleeps in their bed. I know plenty of kids do this, and they are completely justified in being over protective after such an awful year, but I am very worried that this will get passed on to our baby- particularly as they will want to spend lots of time with our baby, and because they have such a big influence on DP. They also pass on advice and dos and don'ts to do with our baby but I want to do things my own way and I'm very intent on getting the baby into good routines, good eating habits and not being spoilt- which are not things they have focused on with theirs. They are lovely, and I do want them to be a big part of baby's life, but I don't want all the over protective spoiling advice, or these things to rub off on the baby. It's all very their way or no way as well.
What can I do to prevent this happening?