Overwhelmed by Membership! Please help?

Okay, I’m just overwhelmed by all the options that Membership has, and confused by how they all interact. I’m not sure if it’s “just one of those days” or what, but I’ve spent a lot of time with WordPress and am just not wrapping my mind around it. So hopefully somebody can help me out. Here’s what I”m trying to accomplish:

Unlike the typical membership site this isn’t designed to protect certain content or certain parts of the site. The entire site is private (it’s for private family communication), except one page that is presented to non-users or non-logged-in users that allows them to login, register, or click to get their own site. Only one person pays a fee, the person who decides they want to “sponsor” the family site (usually the parent/grandparent who’s descendants are using the site). Nobody else pays, but the sponsor. And the sponsor should have the ability to approve users since they know who is and isn’t family (though maybe the registration code will work sufficiently). Can I set things up like this with Membership?

This is where I wish that Membership worked at the Network level. I wish that I could set it up at the network level so that when a new family sponsor signed up to pay the monthly payment, the result was a site created for them. As it is, it appears that the plugin’s settings have to be replicated on each new site.

Can somebody please guide me as to how do go about setting this up? I’ve started some things, but am not even sure I’m headed the right direction. I really need somebody who understands the plugin well, to understand what I’m trying to do, and guide me, or tell me it can’t be done (if that’s the case).

EDIT: to help clarify: The Multisite Privacy plugin has this option “Allow only subscribers or users of the site to view it.” That’s what I want. Then also to make it so new users can register to get access, but only have access once they’ve been approved by the site admin (family member who’s paying for the site), or if they use the correct registration code–either one will work.