Blogs db in WP Multi-site + BP

I have 4 separate installations of WP+BP that I want to link in terms of the members and sites. That is, I want the mbrs of one to be able to see, friend, join groups, of mbrs of the other. I have implemented the moral equivalent of the CUSTOM_USER_TABLE and CUSTOM_USER_META_TABLE method of sharing users. But I need to share sites as well it seems in order to make this work as I really want in BuddyPress.

In particular if user1 is signed up on domain1 they should have a site http://domain1/user1 and user2 on domain2 should have http://domain2/user2.

When I look at the users list as the superadmin I should see the username, Name, Email, Registered, Sites — but the sites should be the actual URL of the site on the actually domain that the person signed up for. Instead w/o the SITE db being shared I see the users but not the actual sites. Actually if I am signed in to domain1 what I see is that user2 has been assigned as a Subscriber to the main site on domain1.

So I think in the WP Multisite databases there are two tables, wp_blogs and wp_blogs meta, that contain information for each blog created. I think I have to merge that database across the 4 installations.

And there are wp_site and wp_sitemeta for each site. I am not sure what role they play.

And then there are the wp_bp_user_blogs and wp_bp_user_blogs_blogmeta might play a role somewhere somehow.

Can you help me think through this problem and let me know what else may need to be done to get to what I want.