There are several restrooms aboard the ship, mostly on the deck one level down, near the main lecture hall. Also, for most cruises they put aboard a big selection of porta-potties. Usually these are on the starboard side just forward of the main gangway. On seating, the main deck has several choices. There are wood-slat benches in various locations, and for most cruises they set up several clusters of folding chairs atop the cargo hatch covers. Below decks, it's mostly folding chairs. Look in the museum (forward) or the main lecture hall where they show movies (midships).

There aren't restrooms on board that I could see and the ship wasn't crowded when we were there. However, the main boat area is full of ropes, ship equipment etc and you had to be careful where you stood and not a lot of space for a lot of people. There are benches to sit down on this area though. There are a lot of steps to negotiate so if your 75 year old has mobility issues this might not be the place to go. It is a very interesting ship to see but not great as a viewing platform in my opinion. Hope this helps x