Multisite Search

Hello

I'm about to do an installation of multisites, but I will need multisite search. I'll explain what I need:

• Sites A, B, C
• Doing a search within the site, should also return results for sites B and C.
• Making an appointment from within the site B, should be returned results only from sites B and C.
• Making an appointment within the site C, should be returned results only from site C.

This can be done? Could you guide me?

PS: Sorry for bad English, I am Brazilian and I'm using Google Translate.

Thanks!