Wedding guest list woes...?

My fiancee and I are getting married next month. About a month ago we thought we had settled on a guest list with his side of the family. They werent happy about having to cut people off of the list but they invited over 30 of their friends plus all of the family! (just for reference we only invited 4 couples and my mother 3 because we want to keep it small) So we thought we had it settled but now i have ordered and sent out the invites and they are badgering us daily about adding three more couples to the guest list. We have told them no, day in and day out and we are just sick of it but they just wont stop. I want to tell them right where to shove it but im holding my tongue and hoping for some better advice about how to handle this. Thanks