How to choose next 3D gaming laptop? Need to understand what basic criteria to look for.

First, apologies if this isn't the best community; please direct me to a better venue if so.

TLDR: I need to buy 2× used gaming laptops that are powerful enough for 3D-heavy games -- I don't know what to look for?

Situation:
My kids have used Lenovo laptops for their rooms, and after some years, their gaming choices (BeamNG and other such 3D-heavy games) mean that old business laptops won't cut it. They need to be replaced (the laptops, not the kids!).

Problem:
Back when I was young, I understood CPU and GPU requirements - these days I don't. Help!

• An Intel i7 may be great but it may also be several years old. I don't understand the naming anymore.
• Most normal laptops have integrated graphics which don't satisfy even most basic GPU requirements.
• Real "gaming laptops" are expensive! And I need 2 of them! Gotta find something used, and I have no idea what search criteria to set.