Can I bike two abreast?

Legally yes. Should you? No. You are asking for trouble when you do that.
Are there restrooms along The Loop?

There are numerous restroom stops on The Oro Valley/Tucson Loop Bike Path. Between restrooms on the path and at parks, there are around 50 restrooms throughout the 130 plus mile system. And do not forget there are convenience stores and many nearby locations on our incredible shared use/bicycling path. The restrooms are handicap and family friendly.