My mom has requested that I be her guardian. What is my next step?

You are right that the POA ends with her death. That's why you need to be named executor of her estate. But the POA is important now while she is alive. Your mother may have to take out a peace bond on your brother to try to keep him away. Could your mother relocate to live closer to you? You mentioned your dads social security. Is your dad still living? If so, what is his condition?

Thanks I will look into all of these things.

Since your mother can think for herself, you can't become her guardian.

Does your mother have a will? I would think that with a will that you with a POA could take legal steps against your brother who is taking things from your mother.

Getting a POA in place is a good first step, but the fact that you live far away is problematic. Having the legal authority to act for her will not necessarily protect her from your brother if he is not willing to abide by the law and/or is able to exert pressure on her to give in to his demands.

You don't take away any of her rights but you can make decisions for her when she becomes unable.  You may not need guardianship.

You might look into POA while she's living and having her make you executor of her estate after death. Then you should be able to thwart attempts to steal from her by the bad brother and wife.

I have also learned through research that becoming her guardian means I take away her rights of living independently. She is in no way ready for that.

I have learned from recently losing my husband that once he passed the POA is no longer worth the paper it is printed on, She is afraid that they will get in and take all she has.

First of all I would get a Power of Attorney for Property and Health. Have an attorney by your mom draw up paperwork and take it to her to sign (make sure you get a copy). Also, a lot of states have free attorneys if your mom's income is low, so you don't have to pay for their assistance. Once you have the POA you have say so over your mom and her belongings. I had to do this due to siblings taking mom's money and I am disabled and live 2 hrs. from mom without a car. Hope this helps.