I'm POA for elderly mother. I found out my brother has not been paying her the yearly payment for the contract for deed on her home. Advice?

If you only recently became POA for your mother and she had all her faculties over the last 22 years she's been living on the farm with your brother, then the $600 and $700 a month she was giving out to your brother is her business and not yours. It may seem unfair to you and maybe it is, but if she is in her right mind now and was then, well it's her money. She can spend it however she wants. If your brother and the farm are in foreclosure then there is no money to get.

Also, just because you are a POA, you do not have the right to write a check out on someone else's checkbook.

According to the “State of Wisconsin Department of Health Services” handbook, “A life estate is created when a property holder transfers ownership of the property to someone else and RETAINS THE RIGHT to live on the property and (RETAINS THE RIGHT TO) the INCOME from it. The new owner of the property is referred to as the remainder person.”

If I understand you, instead of getting yearly income from the farm harvest each Fall, your Mom elected to receive a specific amount annually from your Brother via a “Contract for Deed”.   

Who is foreclosing on the farm—a bank? You need to read your Mother’s “Contract for Deed” document very carefully. If your Mother is the “Vendor” that your Brother purchased the farmland from, then it is possible that the farmland could/should return to her possession. Or is the foreclosure occurring via a “Foreclosure Sale”?  

You need to contact an elder care attorney ASAP who understands “Life Estate contracts” and “Contracts for Deeds” as this situation is very, very complicated and you need professional help from an attorney.

You are her financial POA? How in the world is it that you are writing out a check of 600 to 700 a month every month on brother's bills, without knowing it? Or does your 94 year old mother still have a checkbook on which she is writing out these checks? I don't understand. I do understand his not paying her if the life estate says "while she lives on premises" as with many reverse mortgages, but clearly you need to read the contract. I also understand his not paying her if he is in foreclosure and not paying any creditors because he has no money. This is lawyer work beyond what anyone on forum can advise you of. Your mother will enter the list of creditors on foreclosure I would imagine. This is why something like this should never be done. As POA it isn't your fault. If your Mom has no dementia you even do not have a lot of say in all this.
So it is time for you and brother to see a lawyer together; if he will not do that it is time for you to see one alone. You need the facts and the options now for your Mom as her future funds and care may depend upon it.
So sorry you are going through this.