Thanks for all your answers, guys!
Yes, we wanted to have the ability to use the mount PC in combat (and outside too :P) so I think we will just add the -2 to attack to the mount, and have only one of the players (rider or mount) use a move action per round.
Cheers!
As a druid with wild shape, can I shapeshift into a mount-class animal such as a horse?
If yes, are there any requirements on the behalf of myself or the rider that need to be met?
Cheers!