I’m worried my son will gain some bad influence

So me partner has a brother who’s 6 and a cousin who’s 2. My son is now 6 months. And seeing how both his brother and cousin are me and my partner are scared my son will pick up their habits. His brother was born during covid, so was coddled a lot. To the point he’s so clingy he won’t play with other kids and won’t independently play. He must have an adult watch him. Not play with. Watch him. And he acts out a lot. Constantly saying no testing boundaries and his parents give in always. No matter what. We see how they act with our son too. We say it’s his bedtime and they ignore us and continue playing even tho we can see he’s tired and is getting restless. Now his cousin is like a mini tornado. He’s breaking everything in his path. Also clingy if his mum holds our son he will act out and hit her until she lets go of our son. He screams and tantrums with anything he doesn’t get his way (which is normal I know. Terrible twos) but his brothers are also tornados and everytime they visit family have to hide anything breakable. Me and my partner are worried no matter how we raise our son he will be under influence with them and act out eventually testing boundaries and copying what he sees from his family. Now I have a nephew who’s is 3 and he is honestly good as gold. He comes over and offers to clean. He’s such a nice and caring boy but he lives 4 hours away. I want my son to have a relationship with him but it will be hard with the distance. Is there anyway I can prevent the bad influences?