How did pilots pee on Rutan Voyager?
Did pilots have a separate toilet room for when they needed to relieve themselves?

Given the size and weight of the aircraft, this would be near impossible. There wouldn't even have been margins in the weight budget for toilet paper, let alone a toilet room.
I don't know if there is any official documentation about their bodily fluids.
I did find this quote:

Rutan even brought a small plastic bag with an adhesive, circular opening to answer the question he said he is often asked first—how did you go to the bathroom?

So, the answer seems to be that they glued a plastic bag to their bottoms.

How much room did they have to move around anyways?

Practically none. The aircraft had room for exactly one thing: fuel. If there had been room to move around, that means there was room that wasn't being used for fuel, so they would either have designed away the room or filled it with fuel.
The pilot flying was lying in a lightweight pilot seat, the pilot monitoring sat or lay on the floor next to the pilot flying.

Is there any visual with the interior of aircraft?

Yes, there are quite a number of photos, which you can easily find using your favorite search engine, for example:

Dick Rutan and Jeana Yeager in Cockpit of Voyager
Rutan Voyager Cockpit
Jeana Yeager