If your DD isn't into princesses because it's not her thing, don't push it. If she doesn't really know about them, you can't really know if they are her thing or not. As far as your DS, he might enjoy meeting them more than either of you think. My DS is 4 years older than DD. He loved seeing his little sister so excited meeting them. The princesses were always very sweet to him too. At 16 and 12, they both still enjoy getting their pictures taken with characters.
When we were there last month we saw Aladdin and Jasmine in Aladdin's Oasis. Kids went over to get their picture taken with them. Jasmine was fawning over how tall and handsome DS was (he's 6'6). Finally Aladdin said yes Jasmine, we all can see he's tall, and I guess handsome, if you're into Goofy. Aladdin was standing on his tip toes trying to be as tall as DS in the picture. It was hysterical.
I still tease my sister about getting caught not eating her veggies at that restaurant in HS at WDW and now my kids (who have heard the story) tease her too.
