It would help if you got the model right, and an exact one at that. As the others said, "iMac" isn't a mac laptop, but an AIO desktop.
From the thread I gather you have some model of MacBook Air, that looks like this:
I run linux on one of these. Everything worked out of the box, except for wireless. See my 2-part adventure for how I solved it.
Mac "bios" isn't exactly how you'd expect from PCs. Hold down alt key during startup to enter boot menu, and you're good to go.
If your family member was a mac user before, they might be most comfortable on Gnome, as it has aped many ui features from mac os. It has a similar dock, fluid trackpad-friendly navigation that works the same way, and more.
I tried to do this before, but it did not work out.
I couldn't make the meta key alone open overview. I also tried to add a dock there, but I can only have a panel when not in overview, which is the opposite of that I wanted. I also liked the notification menu and the quick toggles menu in top right corner.
I have been planning to get into plasma extension development to fix some of these issues.