Outdoor Advise

I have two cats Peri (1Y) and Cargo (4M).

They absolutely love going outside (on a harness with me only) but I can’t take them out together without pure chaos.

I was thinking about trying to set up a playpen or a run in the big grass area in my apartment complex and just undoing it/moving it inside with me (with me out there with them the whole time) but wasn’t sure if that was feasible or a thing you can really do with cats?

I live in a second floor apartment without a patio otherwise I’d get them a good catio setup. I want to make sure they’re getting quality outside time and if I can get them both at once that’ll save me some time!

Any advice or ideas would be awesome!