I need to use Billings to bill common clients for the time of more than 1 person - each with a different billing rate. Is it possible to do this?

You can create blueprints, they are basically a slip template so you don't have to always re-enter things that are usually the same like a rates for each person.

So you can create a blueprint for each rate and name it accordingly, the name can represent the person who worked on it if the client needs to see this on the invoice.