Bully

My nephew is a total bully and brat. My son has been over to play with him two days in a row and nearly the whole time he is being bullied. I've tried to get my son to defend himself but he is just too sweet and has been taught better. The other child however will push him, take toys whether they are his or not, on top of trying to do the same thing to the adults around. His mother will tell him she will whoop him if he does something again and when he does she doesn't. If your child was dealing with a kid like this what would you do? I've tried to let most of it go as it wont hurt my son and they need to solve it on their own or it wont really stop. The kids are toddlers under 5. I don't want to over step my boundaries but I am also beyond tired of this boy being allowed to act like he does if he keeps on with this behavior one or both of them will get severely hurt