What has happened to us all that we need to blame other people all the time? We are in a pandemic, all this "they should do this/that/the other" is wrong. People can make up their own minds.
I'm a teacher, I had the vaccination, do I judge those who choose not to? No. Their choice. I did twice weekly LF tests at during term time, but have stopped them over the Easter holiday, because I want to, simple as that. I will do one Sunday night before returning to school. Is is right or wrong? I don't care, I have decided, as an adult, that it what I'm doing. I've seen no one outside the immediate household, so have weighed up the risks and made a decision. It's what we do. OP's parents didn't have the vaccine - their decision, their right, their choice.
OP, the concern here is that your parents have Covid, so focus on supporting them and fingers crossed they cope without being too poorly. Sorry about your DH's birthday, but it's not the end of the world, really is it? An adult's birthday celebrations can easily be postponed for a few weeks.
A little tolerance and acceptance that we are all different, and less jumping on people for doing what they as adults have the right to decide, would help us all I think.