The reason why the A-Wing that Kanan and Ezra use has room for both of them is because it is a trainer model.
Maul uses Mandalorian droids that were designed for an uncompleted arc of Star Wars the Clone Wars. They are based on the rickshaw droid seen in Star Wars: Episode II - Attack of the Clones (2002). Maul's base was designed for the 'Son of Dathomir' arc from the same series which also remains unfinished but was adapted into a Dark Horse comic book series.