If so, then no, you can't get rid of the others.. Although SpyDoctor was long on the "Rogue Anti-Spyware" list because of "false postives" which lured users into buying the software, it appears like it's been removed.. It's STILL listed as one of the "Knock-offs" to either Ad-Aware or Spybot. (Use the other free ones instead.) Still, it's an antispyware tool and not an antivirus tool. Norton will need to remain as the primary antivirus scanner and with antispyware tools, it's always a good idea to have more than one on the machine.

My advice is to leave the two you already have running as the "real time" scanners. Use SpyDoctor as a secondary scanner which you only use for manual scanner. Disable it's "real time" scanning.

Hope this helps.