In laws

I've been with my boyfriend for a year now and his mother seems to really adore my son, though has never once wanted to spend time with him like having him for a night or even just taking him out somewhere. Only when there is some holiday or family event going on that we go to does she pay attention to him. My boyfriend's grandmother is less affectionate and even when we are at any event she is all over his sister's child and over all not paying attention to my son. Neither of them come to visit even though we live right across the road from his sister, whom they visit quite often. It bothers me a great deal. Not so much that they don't come see us or seem to not want to spend time with my son unless he just happens to be near them. It's that they do these things with my boyfriend's sister's son in front of my boyfriend, me and my son.