An unusual domain/subdomain setup for multisite?

I’d like to ask a strange question re multisite please.

Are the following domain names and/or setups possible on a multisite setup (using sub directories, not subdomains)? Essentially we want three sites for the domain and three sites for the domain but can’t figure out how to do the last two on the list below (it may not be possible).

Main Site =
Subsites wanted: = main site = = = = ??? ( = ??? (

We don’t believe subdomains are the answer here because we want the search engines to think of it as 2 or 3 sites. Example:
= one domain in search engines
= three separate domains in search engines

Thanks for any help you have ahead of time.