re: 2 astronauts
Teams of 2 make sense...but, a whole crew consisting of only 2 people? There probably are EVAs that would need 2 people outside and you need someone as safety/observer.
If you plan on sending people to Mars you might as well send enough to do some serious work.
At a minimum 4 up to 20 or so...
I would make the mission one way by design...with the option to return if wanted or needed.
--Chris Vancil