I have a POA for my mother's life estate. How can I protect myself?

From your described situation, it appears that so long as you follow the responsibilities of the POA, you should have little personal liability. You are basically acting for your mother in accordance with the life estate which your mother authorized through the POA. Your brothers may try to force you to act against the interests your mother, but you are should act in the interest of your mother as required by the POA.

You not only need counsel to protect yourself, but also to advise as to what to do with the house. I assume that the three of you are the remaindermen on the deed? If your mother is receiving Medicaid benefits currently, which it sounds like she is, then those benefits would terminate upon sale of the home. The house is an exempt asset for Medicaid purposes, but the proceeds from the sale of the house are not. So if the house is sold, Medicaid qualification would terminate until the proceeds are spent down. It is hard to see how this would be beneficial, but an understanding of the entire situation is necessary, before you can make any decisions on how to proceed. Based on your facts, it sounds like you need to discuss this with a Massachusetts attorney, as soon as possible.