Juggling and compromise and standing yout ground if need be. A little white lie here and there can also help. I'll give you the run down of my March-June.
My moms bday
My Dad's Bday
SIL bday (2 days after DHs)
My Bday (memorial day weekend)
My sister's bday
So as you can see there is basically something going on almost every weekend for 3 months. Then we have to try and find time to do what WE want and it gets crazy.
In the past we have struggled with this a lot. Fights and everything. But we finally came to terms with the fact that we can only do so much. Our parents live 90 mins from each other, and his parents are over an hour from us, so it's impossible to do 2 in one day. SO we don't. We try to rotate. We also try to visit one mom ON mother's day and one on the Saturday before if we can. Same with Easter and the other holidays.
We put OURSELVES first, which I know sounds awful. But if we had a rough week and just don't feel like taking the drive, we don't. We try not to schedule too many "optional" events around this time too. We also try to block out at least one day or night a weekend where we don't have plans. This has been helping and it doesn't feel like we are running constantly. I am sorry, but weekends are ME and US time mostly and I definitely try to adhere to that, and we stopped feeling like we have to be someplace b/c we are expected to. (that was mostly DH anyway and he has gotten totally better at this)
There is nothing wrong with telling a family "sorry we just cannot make it" to an event that isn't a major holiday. Its about you and DH now and you need to remember that! :)
New Jersey: We have dumps, bays and cement boots and we know how to use 'em