Tarkanos

A good friend of yours is willing to kill/maim people for money?

Alka-seltzer.

The video he posted said that jellyfish first aid is vinegar, which stops unfired venom barbs from firing.

Edit: That video has been found wrong by the actual author who posted the above video, so yeah. No vinegar. No pee. Now the best way to stop the pain is to kill yourself.

In the video, a woman stung on the back of her hand is hospitalized for 2 weeks.

No, that's not how that works. It isn't really fair to judge a person for being unable to deal with taking care of others that they didn't sign up to take care of. People are allowed to have their own preferences, lives, and deal-breakers.