allow multi-site user to create blogs too

Here's my main multi-site:

I want to allow some of my multi-sites to create more sites under their subdomain: for example, = first level user site under my main domain ( Is there one of your plugins that allows the next user to be: Is this the path that is created?

I further want to be able to add a Membership and/or Marketpress function to this final user site ( where I as the main domain owner ( can charge a membership fee. I think Marketpress can be set up and the fee shared through Paypal, what about Memberships? I don't think they can be split up between main domain owner and the first level user site, right?

Thanks, Joe.