For California; healthcare power of attorney; do you need both two witnesses and notary? Can I make all medical decisions as my husbands agent?

You need EITHER two witnesses OR a notary. If the person is already in a skilled nursing facility when they're signing the document, the ombudsman from the facility also needs to sign. If there is a valid healthcare power of attorney, you can make all decisions when your husband cannot make them himself. Your husband always has the right to make his own decisions if he's able to.