[tanksoldier]

Depending on your Mom's legal status with regard to Grandma she may be able to prevent these hospital visits by Auntie and may be able to get a restraining order if there are witnesses to the threats. Recording them is even better.

Also, in most states making a threat with the apparent ability to carry it out is assault... and making threats in general can be illegal several ways depending on your state laws.

OTOH, if your Aunt makes some veiled mention of your Mom's safety you can always tell them not to worry, you CC and will be escorting Mom around for the forseable future.