Worried Sick About My Parents and Feeling Guilty

My worst fear is coming to life: I am afraid that my parents (84 and 89) caught COVID because of me. It was my birthday July 14th and I invited them to celebrate with me at an outdoor restaurant and watch a firework display from there, afterward we would all spend the night in a close Airbnb.

Although it was all outdoors it was very crowded. I can't think about anybody looking sick or sneezing other than a guy blowing his nose a lot on my 2 hour bus trip to meet my parents in the morning of the 14th. He was about 4 rows ahead and on the opposite row. I never got close to him until just a few seconds when he passed by us to get off the bus at our same stop.

I wasn't too concerned though because I doubt I would get it from this guy and pass it to my parents just in the 24 hours I would spend with my parents as I would need to get it first.

My parents looked overall healthy other than my mom getting a bout of coughing when she took a nap in bed that day but this isn't too unusual.

On the 15th morning after a shared taxi ride, I left and then on the 16th morning my parents went to say good bye to my cousin and uncle who were visiting our country from the US and my parents didn't have the opportunity to see them during their 14 day stay. So they went to say good bye, when my sister overheard my cousin telling another relative, "for the first time today, I am finally feeling better and am no longer congested." Then my uncle showed up and he was really weird, my mom said he looked visibly sick and was tired and not talking much which is not like him.

After that, today, July 17th morning, my mom reported feeling nauseous, very tired and no appetite. She told me she had a hard time keeping her eyes open. I was worried about her getting a UTI because she gets it without the typical urinary issues but just mere weakness and a mild fever. My sister took her temperature and it was 99.6 when it's usually 96.8.

She only ate some grapes and 4-5 crackers all day. She has been in bed all day and taking paracetamol. Next, my dad said he has a headache which he never gets so he took some paracetamol too.

I wonder if they could have gotten it from cousin and uncle within just one day. I am afraid if it's my fault for letting them celebrate with me in a crowded place. They go to church every day and take risks, have been close to people coughing and never got it other than once, but then one day I decided to celebrate, they apparently got it, what are the chances?

I can't recall them being exposed to anybody being sick although it was crowded no body really coughed or sneezed nearby and in our area there are very little COVID cases (we are in Europe). I feel exhausted, feel like crying and it doesn't help that I am a two hour bus drive away and my sister who lives with them just went to bed instead of checking on them as she said she is super tired. They got the 3 boosters 3 years ago and skipped the 4th booster at the end of 2022 because they got covid. Tomorrow hopefully my sister will have them to an in home covid test.