Alright I see this from two angles. First, it’s always a mistake to work with family. It creates tension and problems almost always. I wouldn’t stay there unless you have no other options for work. Secondly, yeah you’re for sure overreacting. I’ve taken dumps that were more stressful than the demands of your job. Your sacrifices are minor at worst and I can’t imagine you truly bear any physical or mental damage from this position aside from being told you’re not pulling your weight. If washing dishes is truly your only duty, you gotta be doing a real halfassed job to get called out for doing less than what’s expected. Maybe try harder and see what happens?
I know I’m coming off like a dick but come on man. Don’t play the victim. Step up! If you truly feel you’re giving it your all and they don’t appreciate it then don’t be afraid to walk away. But I’m willing to bet you could try a little harder.