If you really want rights, you can file for an emergency guardianship in order to get information and direct his care/make decisions on treatments.

You can also file for guardianship of assets, if he has any. This could be called a conservatorship or an administration or something else—it varies by state. This allows you to do anything he would do with his money, assets, apply for disability/state benefits, etc.

The above is expensive unless the court where you are offers help with making the filings.

Regarding his state—it hasn’t been very long, and there are a lot of drugs yet to try.