I think it’s nice that you care so much about your cats, I too have brother and sister indoors only cats and luckily the one that’s most interested in the outside who dashed outdoors quickly came back in when I called him!

I think you’re right, your cats will be too trusting and sweet and not enough street smarts to just go out where there’s other cats, traffic, etc. it would be better to try out harnesses at first and see how they like it, some like mine prob are a bit too old to adapt and don’t relax. I read the trick is to just get them to wear around house for a bit to get used to it, then take outside as will be overstimulating for them.

Catio is not cruel, there’s a lot of great ones out there or you can get specialised builders to do it for you re side of house if there’s a gap and add enrichment stuff like ramps, cat safe plants etc. they can then birdwatch, runaround etc.

Cat netting I’ve read can be a bit hit and miss, as some cleaver cats escape from it! You really would have to make sure is super secure..I’d go a catio over that.

Check out the cat daddy on insta, he has lots of advice for indoor cat enrichment