Do you have anything prepared for this? Do you say, no but come back in a week?
Do you say, yes, here are four pre-gen character sheets, let’s play a random short one-shot?
Do you say, no we’d need to spend time prepping for D&D but here’s a simpler tabletop game which uses minis and dice, let’s play this right now instead? (for example, Shadowdark)
Or something else?
When I was younger we played role played so much over so many different systems that we eventually would just “play” any world and scenario we wanted. D20 for skills and resistance, d6 and d10 for damage and percentage spreads.
We didn’t need a lot of rules because we knew how games worked.
Eventually others would join us and be playing right away because we weren’t a bunch of rule lawyers.
If approach it like that. Very simple subset of rules to get them playing without fussing over everything.