Bridesmaids Form Hell (What Should I Do?)

I just talked with my maid of honor and she explained to me how to of my bridesmaids had made comments that they were going to back out of my wedding. These I thought were very close freinds of mine and I never thought they would do something like this to me. I have already purchased their gifts and I have groomsmen for their partners who have already payed for there tuxedos. I don`t know what I am going to do but I feel so uneasy I don`t know how to approch the two of them and my wedding is in November. What shoul I do? I really don`t want to go off on them they are my freinds I just don`t know how to go about it.