When running multiple VM's & using using th mac as the same time, the keyboard may behave strangely, keys may not as expected through ALL vm's and the mac host. Trackpad button may be unresponsive on the mac. Workaround: shut down all currently running parallels, and restart.
Are you sure, though? Did you actually look at your Activity Monitor to see how your resources are being allocated? With certain apps, you can max out 16GB of RAM no problem...
