I have built a number of sites on my wp multisite install

Hi, I have built a number of sites on my wp multisite install and would like them all to be buddypress communitites that work together but are also stand alone sites. They are all built under my main site as additional sites. The main site is a buddypress community but the others are not. I assume because the plugin is being used on the main site. Is it possible to use the buddypress plugin on all my sites in a multisite installation or do the need to be separate installs. In addition can I give a registered user on my main site access to the other communities under one login, like how I have access as the super admin? If you could tell me how to accomplish this i would really appreciate it.

Thanks !