Documents for Traveling to the USA for treatment

Hey all, I've decided to travel to Florida to the sponaugle wellness centre to get treatment for my lyme and co.
I live in the UK (born also) and have a Full UK passport, I was just wondering what kind of visas and documents I need, I've came across so many e.g ESTA, Medical Visa, Non-imagrant Visa etc. Im not to sure which one I apply for as its for around 6 months of time needed

Also I'm travelling with my brother who will be looking after me whilst I'm over there, is there something different he needs to apply for as he's not the one being treated?

Passport is only valid up to 90 days so I hear, I thought US and UK were quite lenient on travel, I guess not.

I've genuinely only heard good things about the SWI, are you able to give me access to any negative reviews or own experience of the place ?