I've had similar issues with both my mother and sister about my two sons, my sister was awful about my elder son and my mother has gone so far as to tell people that she has 4 grandsons when she actually has 5. In fact, they've both been horrendous to/ about me too.
I've spent years trying to sort it out with them, trying so very hard to find out why they feel the way they do and telling my boys along the way that sometimes people get weird ideas into their heads and that eventually they'd realise that they were wrong but after almost 20yrs of doing this my boys have grown up and have decided that they don't need such negative people in their lives. As a result, neither of my sons has any contact with my sister, my younger son only exchanged birthday and xmas cards with my mother and I've had no contact with either for a few years now.
I truly wish we'd been able to straighten things out and have good relationships across the family but this was not to be for us and life for the three of us is so much better without all the negativity.
I would suggest that you give your brother a wide berth for a short time, maybe he'll realise what he's said but the next time you do speak, remind him of what he said and let him know that he was wrong, your son has done nothing to deserve losing his job, we are in the middle of a worldwide pandemic and thousands are losing their livelihoods but also point out that he upset you by saying it too. Hopefully you'll get an apology and be able to get back on track but if he maintains his position on the subject, be prepared for your relationship to suffer. You are right, he's the one in the wrong, so you shouldn't really be the one having to chase him, he really should be coming to you with a sincere apology!