To drive a DC motor in two directions you'll want an H-bridge. These can be controlled by a Pi, no problem, as long as you have a separate power source (or the motors are tiny, which in your case they will not be.) Look around and check for one that will handle the amperage that your motors need.
If you're trying to control it by degrees, you may be looking at a stepper motor or servo motor instead of a DC motor. The Pi can control either of these, but again you'll need a separate power source for these, much like with the DC motors, and probably separate electronics.
The motor wouldn't be online... but the Pi controlling it probably would be, unless you want it to only work through Bluetooth or a local network (not connected to the Internet, but with a local wireless AP that the phone can connect to for controlling it.)
Two motors should be no trouble for one Pi, so long as you have the correct control circuits. A single Pi model B+ has 26 GPIO pins, which should let you control up to 13 DC motors using a H-bridges if you do it right. The number of stepper motors will depend on how many coils in each motor. Most have 4 I think, so you could use 6 motors with a single B+ if I'm right about that, with 2 pins left over for other purposes. 2 LEDs, one DC motor on an H-bridge, 2 switches, etc.
Check out YouTube for videos on how to make the Pi control whatever type of motor you'll be using. I'll warn you ahead of time that the Raspberry Pi Guy's H-bridge tutorial has a mistake that has burned out a few peoples' Pis: The "four enable pins" are not all enable pins and two of them carry 5v, so find another video to explain which ones and how to properly connect that type of H-bridge. Other than that his videos are very good.