Restricting multiple sign up and pulling child theme

Hello.
I just started using the Membership 2 plugin. I have 2 question for shich I can not find documentation.
1) when someone registers they are able to set up a multi site. How to do ensure that only the people that pay can set it up, and more importantly that they only set up 1.

2) How do I get the new multi site to pull the child theme automatically?