McAfee disables the Windows virus programs such as defender. Any thing that has a real time scanner is not recommended to use with McAfee as it may clash.
I have not seen McAfee disable programs other than the windows versions so best to either not use them or disable the real time scanning function of the non McAfee program.
Moved to VirusScan for better support.
Yes - having 2 anti-virus engines installed can cause problems, even possibly letting infection in.
There are some 3rd party tools that can be used safely to supplement your protection.
See the link below under Free 3rd Party Tools.