They live in Illinois - I live in California

My father just reached age 65 and has a long list of health problems. My little sister is autistic and has been disabled but she is now 18 years old. My stepmother is 61, she has a lot of health and mental problems, and she can't manage basic tasks.

My father wants me to take care of my sister and my stepmother when he's gone. He has written a "Will" leaving everything to me, and we have had extensive conversations about his wishes. "That I do have him note down."

My question is, because my sister is 18. Do I need a power of attorney or something to make this process less of an issue? She is low functioning and will need help for the rest of her life.

Also, do I need anything from my step mom, such as a release to the estate and / or a power of attorney.

Basically, when he goes, I'm to help them by managing money, health care, and other living expenses. My father doesn't have much money or assets. He want's to make sure they are good without him.

I have made him a promise that I will always be there for them regardless of his estate.

Please help. I'm lost on what to do here. Any suggestions are much appreciated!

Also, I intend to invest any leftover money from the estate / social security / disability and put the investment accounts into a trust for my sister's retirement / emergency fund.