Piston w/o tanks

Can you have pistons with no pnumatic tanks and still have 2 additiinal motors?

Nope, the relevant rule reads:

Since a piston is still a pneumatic component, you can’t use it without sacrificing the motors.

If the only reason you want a piston is to use as a spring, it shouldn’t be too difficult to create your own mock piston out of linear slides pieces and rubber bands.