Sounds like my schedule!! We had MIL's bday two weekends ago, SIL's bday this past weekend, then mother's day and my mom's bday 2 days after Mother's day.
We did what the PP's said, you just juggle it. We saw both MIL and SIL on their bday's, we'll see my mom for mother's day on Saturday, his on Sunday, then my mom again on Tuesday for her b-day. Makes for a busy schedule, but this way no one feels excluded.