Long distance family coming for the birth!

Anyone else's family live out of state? My mom and grandma NEED to be here for the birth, but how do we plan for that? You never know when he'll decide come! My mom will be staying a full week(maybe longer) but my grandma just wants to be here for the birth and a couple days after. I always fly Southwest who has no Change-fees, but it's hard to plan the dates that far in advance. And tickets will be outrageous the few days leading up to the birth. Anybody have experience with this??