The best thing to do is take the power of attorney document to the bank with which you want to do business and ask a bank representative each of your questions. Banks being banks, most have their own rules and will be happy to explain them to you.

Chances are, you'll be instructed to open the account in your mother-in-law's name and asked to sign checks with her name followed by your own, including words such as "under power of attorney" and the date of the document or simply, "POA." But the bank will tell you exactly what you need to do to open and manage a bank account on your mother's behalf.