Are you the youngest in the family? If you are, this could be one of the reasons they think they can domineer you - always the baby of the family. I'm the youngest of my siblings and I don't get along with my sister for that reason. I think once the siblings all grow up, there shouldn't be any hierarchy because of age difference and everyones on a even playing field. My brother is 14 yrs older and he's the oldest, but he's always treated me respectfully even when I was a kid.

I think you need to learn how to nicely assertive and stick up for yourself. You need to be consistent and one of them will probably wonder what's happening and that's when you should explain, you're tired of always giving in. Maybe you could even do some role playing with your husband - he could pretend he's your sister and you can practice being assertive. Good luck