She writes to Dear Abby: my sister has been planning to retire and move in with my husband and me…. She is a strong anti-vax advocate and refuses to get vaccinated for COVID.
I agree with Dear Abby and your husband that it’s a definite NO unless she gets vaccinated. But there are other reasons she should not live with you even if she is vaccinated. You sound like sensible people and your sister is not. Do you really want to spend the rest of your lives arguing with her about the pseudoscience that she believes in, and the deplorable political candidates she most likely endorses? It doesn’t sound like a nice retirement to me.
Being anti-vax is not OK. Tolerating someone who is anti-vax in your home is not OK. Don’t do it.