This is easier than getting the load balanced between multiple 7805 regulators.
http://www.national.com/mpf/LM/LM350.html
3 amps with heat sink.
Use the LM350 for the motors and a 7805 for the PIC.

If you still want to parallel the 7805s, bend the legs so one heat sink can be attached to all of them at the same time (chips side by side) . The legs should be bent enough to allow at least 0.20 inch traces on all legs. Do not use a set of capacitors for each regulator. Put together as stated and you have one big regulator.

Or you have a bad 7805.