3 different domains – same users,etc

Hi. I got a question to ask.

I’m in need of 3 separate domains. If user registers in 1 of the sites then it automatically registers on other 2.

WooCommerce – works on all sites. If the user has money in one of the sites then he can use it on other sites.

Basically what I mean is that all 3 sites will have different content (items) but I want users and all the other things to be as one. So if a user has money in site 1 he can use the money in all 3 sites. I’m not sure if it’s possible, maybe I need some additional coding, could you give some tips on where to look and go?