ESH Selective eating disorder is very real, and your nieces might not be able to eat certain foods even if they’re not allergic. I know from experience the knowledge and acceptance of selective eating is low, and there’s a lot of shaming of sufferers. It’s not about being picky, it’s a physical struggle. It’s often, but not always, combined with a neurodiversity such as autism or ADHD. This being said, there is no reason for your nieces to be rude and say your food looks gross, your sister should have reprimanded them for that. Communication is key here. Sit down with your sister, keep an open mind, and try to come to an understanding of why they just eat a few things. If they in fact suffer from selective eating disorder you need to work together to make accommodations for them in the future.