When Mom passes does sis still have POA and what can she do with it?

Right now I am treated like the next door neighbor's second cousin, twice removed. Like I am not a person.

Well, if you continue to cave in you already you have you answer. If you continue to cave in.

Mother has a will. Sis and step bro are executors. But of course bro will be treated like a non person. We all cave in to sis demands.

It's possible that mom has no will. If that's the case, who will be paying for these final expenses? That is most likely the person who will be calling the shots on arrangements.

After your mom dies, legally, the Executor of her will is in charge of most of the things you mentioned. She is obligated to carry out any instructions outlined in the will; sans instructions, since she controls the purse strings, if she's so inclined, she can control everything else regarding your mom's funeral. Her rights and duties as power of attorney expire at her death.

As far as being treated like the next door neighbor, I have always been treated that way. It has nothing to do with the POA but the dynamics of your family relationship. My brother lives near my mother and I live 11 hours away. I have had zero input into mom's business and am her POA alternate only because my brother refused to put his son on the POA alternate. So I guess if your sister wants to leave you out of the loop all you can do is protest, loudly. But good luck with that because it has yet to work for me.

No, POA is no longer valid when your mother dies. Is she executor of your mother's will?