The potential for outright scams is high. With eBay purchases, you generally won't be able to see the unit (or units) until they arrive at your door. That certainly applies to eBay, Craigslist, and Facebook Marketplace purchases. Let's cut to the chase: Buying used gear can save you money but can be risky as heck. Since graphics and video production are some of the Mac's strengths (and Chromebook's weaknesses), I'm going to assume that the kids need some video and graphic capability - and machines that can handle that load.
It could be his kids prefer MacOS, or it could be that they want some features or applications unique to Mac laptops. My correspondent also didn't specify why, specifically, he was interested in MacBooks rather than Windows laptops.
His 2011 Chromebooks are a bit long in the tooth, but there are some quite fine 2020 Chromebooks to be had quite inexpensively. Unfortunately, my correspondent didn't detail why he wanted to move from Chromebooks to MacBooks. These dozen laptops can keep you online and working longer when you need to be unplugged. The best laptops with the longest battery life
