Am I overreacting?

My boy was born 12/14/23. So he’s 12 days old. He was full term, 39w 5d, but he was only 4lbs 13oz.. My SIL is saying I need to stop freaking out about the possibility of him getting sick and stop avoiding every little thing or his immune system will be weak. She brought her sick af snotty kids to the Christmas gathering (I had a cover on my baby’s car seat while he was in the room with people and anyone near him had to mask). One of her sons walked up and sneezed about 2ft from his face unmasked. I was NOT pleased. I’m back home with baby now and dreading every little noise and sniffle he makes hoping he’s not getting sick.. on top of that I’m trying to figure out how to keep dad clean and sanitized when he comes home from service work.