The guests knew they were sick and should have just stayed at a hotel. A sniffle is clearly a lot different from what the OP’s friends had. I wouldn’t have a problem with a friend staying if they had a mild cold, but clearly the visitors were sicker than that (not covid, if I read correctly). That said, I wouldn’t disown them as friends. People tend to think “it’s just a cold, it isn’t going to be that bad.” We deceive ourselves sometimes.
Last year, freshly vaxxed up, hubby and I visited D overseas. We landed and called her and she said she had a cold. I wasn’t not going to see her. She did a covid test which was negative. I stayed with her for a couple of days while hubby went on a short work trip. We tried to not share too many germs, but I did get her cold (tested, not covid). Hubby didn’t. I probably spent 4 days with her, while hubby only saw her for two days. We were overseas for about a week and flew home double masked (which I always do now, cold or not.) I did still have a cold. Should I have not flown home because of it? Hard to say. My ears and sinuses were clear, so I flew home.
My friend went to France to visit elderly friends. Got to the hotel and a couple of days later was sick with covid. She didn’t see the friends. She was very upset about it because they even said it was okay and they could just be outside. But it was winter and she just couldn’t live with the thought of making them sick.
It’s hard to reconcile a strong desire to do something with the reality of the consequences afterwards. Throw in long distance travel to see loved ones, plane tickets, hotels, etc…and people will take what they think is a calculated risk. I get it. It doesn’t mean we should do it, of course. Would I fly or visit friends if I had covid, was hacking and sneezing, and had a fever? No. Would I fly or visit friends if I was getting over covid or a cold, wasn’t coughing anymore, didn’t have a fever, and was masked? I might fly, and would definitely tell the friends I was getting over covid or a cold. Then I’d let them make the choice. However, if the friend or family member was compromised or elderly, I wouldn’t visit until I was testing negative.
Sorry for digressing. Covid is now part of our reality so I feel at this point, we all have to be responsible, but also keep living life.