6/8 cats have gingivitis??

Hello. Recently I've been so stressed out because I've been seeing that almost all of my cats have reddish gums, especially at the back.

At first I saw our one and a half year old cat, red gums, she previously had some kind of bump on her lips that's healed now (I didn't think it was concerning then), and she also has a red spot in the middle of the gums on both sides. I think it's getting better since then, but I'm still worried. And then I checked another cat, he didn't have red spots in the middle of the gums, but he had redder gums overall. And then I checked the rest, they all have very mild redness on their gums at the back teeth only, aside from 2. They're all eating and fine, still doing relatively normal. My only problem is how so many of them have it?? I'm also worried about treatment because dental cleaning for all of them is gonna be super expensive.

Please help! Is it gingivitis or something else? Maybe I'm overthinking it? I'm always extremely anxious about their health and I'm honestly exhausted of myself. I was thinking to observe it in the meantime since the first seems to be getting better, but what can I do in the meantime? Should I separate them? Can they still share food and water?? Thanks for your responses