I feel for you , you would think your sis would be grateful for you , for taking her and her daughters in .
Was your sister alway like that messy ?

I think you need to make some ground rules because she is not respecting you or your home and that is not cool .

I would have her pay rent so your not left paying for everything your sister needs to learn how to take responsibility . And maybe she dose not know how and you need to show her , because right now she is making you do all the work and you will get burned out .