According to ESET's Knowledge Base, there should be NO compatibility issues with Windows Defender. There's no need to disable (or remove) it prior to installation. See ESET's Smart Security Installation Guide. They do note during the installation, you may see some additional prompts, if installing it with the UAC turned on. But nothing else out of the ordinary.
With the free version of Malwarebytes' Anti-Malware installed on the desktop (XP), there should also be no reason to disable it. It's not running in real-time, and shouldn't pose a problem.
ESET's Knowledge Base might help answer any other questions you might have.
Best of luck..
I plan on installing ESET Smart Security to my laptop and
desktop. Laptop is Windows Vista with Microsoft Defender and
Eset Online Scanner. Desktop is Windows XP with only the free Malwarebytes Scanner. Is it necessary to remove them
or disable before installing the ESET Smart? And enable them after installation or ESET Smart will do as good without the others? Will welcome any better suggestions. Thanks.