As wife and caregiver of my husband, and someone who also holds power of attorney over my husband, can I require the hospital and doctors to only release medical information to me and who I designate?

It's HIPAA, but aside from spelling, when you sign any medical form there is fine print (usually right above the signature line) allowing the information to be released to other medical providers. You can refuse to sign it, but why would you? If you have copies of all the forms you have signed, you can go through them and decide which ones you want to rescind. But in general, they have no reason to divulge medical information to any provider who doesn't have a vested interest in the health of your husband.

Your choice. As far as I know, there is no spot for designating which other medical providers are allowed to have the information. And signing a boilerplate form after writing in limitations in the margin doesn't hold, legally.

As Joy said, all US medical providers are required to have patients sign an authorization form designating who they can release info to. Ask his medical providers for a new form for you to sign providing them with a copy of the POA to show you can sign for him.