In-laws are at it, again......?

Yes, I have yet another in-law/husband problem. My sis-in-law mentioned me to that she ALWAYS has 2 birthday parties, one down there shore (which is where we are all going) and one at home. Well my lovely mom-in-law chimed in and said "oh we can have it at your (meaning ME) house." So I laughed it off and said, yea right. Well, they were serious. They call my husband last night and want to know what's going on. Now he knows I didn't want to have anything, there's no need to have another party when we will ALL be there this weekend. And yet again, my husband won't stand up against his mother. So my hubby said sure, come over. So, now I have to make sure my house is clean and go food shopping. And to boot, we will be away this weekend (for party # 1) so I have all of about tonight to do this all. This is just the tip of the iceburg. I am at my wit's end with my hubby and his family. I am so angry, I don't want to say anything I'll regret later. Any suggestions? Thanks!