The current AV's use low level drivers that will conflict with each other even if you are able to turn one or more of them off. I believe the only way is to uninstall the one/s you don't want to use. The others can not remain installed as secondary demand scanners. (I believe Avira - which is good- has an ability for installation without the resident.)
Avast and AVG both have removal tools, that should be run in safe mode, to complete the uninstall.
Avast uninstall utility. AVG Remover.
What PCTools AV did you install? Threatfire will run well alongside most AV's, being a behaviour blocker. I know from experience it works well with Avast.
For secondary demand AV (or other malware) scanners, I'd suggest MBAM, Superantispyware, or Dr Web's Cureit.