I am the Matron of Honor in my best friend's wedding (she was my Maid of Honor) and she is getting married in the summer of 2016 but has not set a date. My SIL just got engaged and both her and her fiance are teachers, so it seems likely they will be getting married around the same time. I am worried that they may end up getting married on the same day or that other wedding conflicts may arise. I think my SIL would be really upset if I did not go to her wedding so I want to try to prevent this from happening as much as possible. Is there any polite and reasonable way to bring up this concern with either of them or do I just need to wait it out and potentially miss SIL's wedding? I don't want it to seem like they have to plan it around me but I know she would be really mad if I couldn't go.