Oh boy do I have in law problems...
My MIL isn't exactly racist, but has said several times to her kids to only marry other Filipino's, I'm white. (also her husband IS white too! 2nd husband) One of the BIL's is always forever talking down on "Americans" (black,white brown..it don't matter) it infuriates me. I just want to scream at him that if he doesn't like us Americans or our culture or whatever to friggin leave!
And one of the things that really bothers me is the favoritism among the children. There are 19 grand kids all together, my husband and I have 3 kids. Well a couple years ago, everyone is at the MIL/ FIL's house. And it comes up that ALL of the grand kids got these beautiful knitted blankets from grandma. All of the kids Except for ours. Can you imagine the hurt on my kids faces when they learn they were the only ones excluded?! My FIL quick to see that told them to "go tell grandma their favorite colors so she can knit them each one". Well about a year later my youngest got hers, the 2 oldest haven't gotten one. (and won't now due to her health deteriorating)
I suggest in your case to just let it go, I try not to say anything to my husband. He has since realized that his family is like this. And it's such a huge family I don't want to start anything... I know how they talk about one of the exes. Oh yea they talk about everyone who isn't blood related! (and not there at the time) To be a fly on a wall when I'm not around.
I no longer really rant to my husband about his family, no sense in making him feel bad or cause hurt feelings. (he knows how they are) I write my frustrations with them down in a diary sometimes blog.
Every now and then I do let my opinion be known, and I do have the attitude to them that if they don't like it I really don't care. But normally I just listen to them praise their favorites and talk smack on whatever daughter/ son in law that isn't there at the time. At the end of the day it's not worth it for me to create some dramz.
Just take the high road, and when they start up when your around leave the room or house. Maybe eventually they will get the hint that you don't want to hear it.