you have let them dictate what happens, poor you I do feel for you.
Dont wait around the corner, either drive up outside and toot up or do the proper thing and dont be the doormat waiting for the call, when they go there take yourself out for the day, do something you want to do and tell them to get a cab home or let the in laws drive them back, you have made it too easy to fit into their plans, stand up for yourself, why does your hubby/partner let them treat u like this ? has he no backbone to stand up to them, they should be begging you to see their grandchildren.
Say I have had enough and here is what I [ emphasis on the I] AM GOING TO DO IN FUTURE, no more waiting around, if you dont like the idea of me going out then dont go, put your foot down, be just as rude to them, as they are to you, see how they like it. Take a stand now, good luck.