This has an episode of “Catfish” written all over it - if you’ve ever seen the show, you would’ve seen there’s people out there who lie about this stuff for YEARS.
I honestly find it really weird that his “brother” is messaging you - if your sibling was really poorly in hospital, would you be spending time messaging someone they were having casual dates with, that you’d never met?
I personally would block but if you want to be nice about it, send a message first and just say you’re so sorry but there’s literally no support you can offer if you don’t even know this man’s last name, can’t visit him and can’t contact him directly. That you wish him the best and hope it all works out and maybe you’ll reconnect in the future. Block. Move on.