I need advice family issue

Okay so my husband 22 were married with a 4month old. His sisters 19 but is crying cause she don’t see her brother anymore. We tell her she can vist when she wants but she just throws a fit. She like cry’s over him and post all over fb she don’t see her brother . I find it kinda weird cause he has other responsibilities. I get there sibling but me and my brother are not like that . We grew up and do other things. I dont wanna be tied him to my brother . What do I do??