Well, if you calculate that the blue carriage with your camera weighs 1.5kg and the centre of gravity is 2cm behind the pivot point, then the torque is 3kg-cm, which is just barely within the holding torque specification of this motor, meaning that motor can hold it but it can't move the camera unless it has some gearing.
Consider also that the CG might be above or below the pivot, which means that the maximum torque will occur when that point is rotated to level with the axle. You can use Pythagoras theorem to work this out.
Take your camera and lens and try to balance them on a spoon or knife on the table. That will help you find where the CG is. If you know where the nodal point of the lens is, then you can work out the distance. The kitchen table is useful because kitchens also have scales to weigh things.
Those drawings don't shout out to me that there must be two motors. The blue carriage must have some rigidity, so driving it at one end will still rotate the whole thing. Unless you were going to make it out of wet noodles or something.
Yes, you can pair two controllers on the same Arduino output pins. That will work well.