in my home desktop, i use Avast as the active antivirus program. I keep two famous antispyware programs installed and occasionally updated -- malwarebytes and spybot search and destroy.
If at times avast detects any virus, usually avast is good enough to delete the virus. But sometimes i also check with Spybot and Malwarebytes. I have not experienced any conflict with having these three programs installed.
You see, Avast is more of the antivirus type that always runs in the background while the computer is on. Antispyware like Malwarebytes and SpyBot Search and Destroy are more of the on-demand programs that run only when you manually start them yourself.