Antivirus software recommendation

The advice you are likely to get in here is that anti-virus software for a mac is a waste of time, there are no viruses that affect a mac. Real time scanning AV apps are just resource hogs and affect the performance of the mac.

Macs come with X-Protect which updates regularly and keeps your mac clear of most adware/ malware. Malwarebytes is often recommended here, I use it myself, the free version. As you are using several macs which may be being used to copy files from USBs or other devices that have been or are going to be used in Windows machines you may want to prevent the spread of windows malware/ viruses etc by using Clam Xav, which is about the only AV many people would recommend here.

You can run malwarebytes (free for Mac) if/when you need it (when you inadvertently got some adware) - it is not an antivirus software. I download and run a fresh uptodate copy when I need it (I believe once in the last 3 years).

Malwarebytes | Malwarebytes for Mac

If you feel better running AV, then go for the ClamXav. Most AV software significantly slows down Mac OS and can cause various glitches/hiccups - I wouldn't have any go near any of my Macs unless there was an imminent threat/problem.

Contacted in apple support many times with senior apple advisors regarding do virus get installed in Mac , they had interacted with a caller who had installed virus in the Mac ( long time back ) , accidentally downloaded malicious software that was embedded with padlocked folders ( example .exe , .db , .bat , .pif , .vbs files ) , but that is very rare , it doesn't mean to be scared and install anti virus in Mac , they will delete important system files .

Malware bytes Anti - Malware for Mac can be used to delete adwares or malware .

See some articles OS X El Capitan: What is malware?

OS X El Capitan: Protect your Mac from malware

OS X El Capitan: Ways to avoid harmful software

You can switch to Malware - Bytes Anti Malware for Mac , and scan the system in few days , while browsing on internet lot of websites are searched , the Mac user is not aware of integrity of all of them .

Some have hidden malicious contents , codes and the user clicks on the links and on displayed advertisements and ,by mistake malware / adwares download in the system .

Some information gathered https://safebrowsing.google.com/

https://searchengineland.com/googles-safe-browsing-diagnostic-tool-14064

The user can only avoid viewing doubtful sites and protect the system .

Downloading anti - virus and using it frequently can delete important files in the Mac , so don't use them .

Another articles for mails Safety tips for handling email attachments and content downloaded from the Internet - Apple Support

Identify and filter junk mail in iCloud - Apple Support

I agree with Eau Rouge. I tested this several years ago and at the time it seemed less intrusive than most other anti-virus programs.

ClamXav