Expert Opinion - Very Complex Situation

I don't know your historic posts, but by this one post, I kinda don't disagree with your husband. DH is just being cautious. Flight travelling is very risky, such that many countries mandate 2 weeks quarantine after flights. So why is he wrong?
If you have an extra room where your brother can stay without coming in direct contact with you all during his entire stay like private bath and washroom - make him stay there.
Ask your DH to consider his staying in your home but being distanced. Even when your brother is home, maintain social distancing , don't come in direct contact with him.

This Covid-situation has made many of us OCD, i know many such people in my life who are as cautious or maybe over-cautious just like your husband. And i have to say, even though i am not THAT careful, i don't disagree with them. This IS the time to be extra careful and extra responsible!! Because even when people survive the viral infection, the long term effects of Covid are scary.