You can customize Sitecore analytics, but you should first break down some requirements for what you want to see within Sitecore Analytics dashboard, and who should see it.
Assume you have a multi-tenant setup like this:
Out of the box, Sitecore analytics collects data per site and allows you to filter per site.
A simple solution, if it meets your requirements, is to not do anything! If you want to view data for Tenant 1, you can view analytics dashboard and select "Site A" or "Site B". Then for Tenant 2, select "Site C" or "Site D".
Or perhaps you have a requirement that a tenant 1 user is to only see "Site A" and "Site B" in their Site dropdown list... for this you would need custom code.
So without any specific requirements, you don't need to configure anything.