Once a DPOA has been appointed and has been notarized can it be amended?

My husband has durable power of attorney of his mothers finacial and health care needs and it is notarized. Mom has Alzhiemers and his mother has been staying with his cousin temporarly and our 18yr old daughter has been staying at the cousins as well taking care of her, we are in the process of moving into a bigger place and trying to buy a home and is taking longer than we anticipated., and the cousin is starting problems asking for a huge amount of money every week and knowing in advance that her aunt and my husbands mom has a little bit of a nest egg and the cousin was on my husband to get his mom back to california well he flew out to Kentucky where she was living and he seemed to think she was fine and her herself said i will be there when iam ready. until the cousin got on the phone with mom's old boss and insisted to get her out here keep in mind cousin is uneducated ,boyfriend works whenever and the cousin has never worked a day in her life has depended on goverment assistance and gets SSI for one of her 6 kids and cousins dad has recently passed away and would depend on his monthly check as extra income, and is threatening my husband to take him to court and she thinks she can now get power of attorney after a durable power of attorney which my husband has and has been legalized by a notary republic and mom appointed her only son to be her durable power of attorney. Once a durable power of attorney has been appointed and has been notarized can it be amended. And what legal actions should my husband take towards the cousin. The cousin is also filling moms head with lies also cousin has used 2 of moms personal checks stated that mom okayed her to write the checks.also mom had $250 on her when she arrived here in california that came up missing 2 days after she was here.