OP, it's possible that the key words in your post are "all of a sudden."

You say your husband's jealousy and animosity are sudden things -- so I'd be asking myself: What changed in my husband's work life, or at home, or in his mental state, that he was OK with brother before and now isn't, all at once?

It's possible of course that husband always had these feelings and they only now bubbled to the surface; did brother quite recently, for instance, win a big legal case (and gets a bonus for it, your DH assumes)? Maybe brother recently purchased something great that finally set off the jealousy DH has long felt but concealed--new house, car, kids are getting some big-deal thing for the holidays, whatever? Did brother or his wife possibly let slip that bro is up for promotion at the firm?

Or conversely, the issue could be at your husband's end and not brother's: Did husband possibly get passed over for a promotion, lost some project to another person at work, has conflicts with his boss, realizes he can't afford to send a kid to some program that kid really would like to attend....Whatever? I'd be thinking through these things to see if there was a trigger or a couple of triggers that set this off.

Then I'd talk to husband and be clear but gentle, too, because he might not really realize how strident he sounds when he carps about DS and he might not be able to admit that he's jealous, now or ever. But I'd tell husband that "When you say X about brother, I feel Y" -- yep, the classic construction for telling someone he is being a jerk without saying "You're being a jerk." If you are close to your brother and see him and his family, this does need to be brought out between you and husband and even if he would never admit to jealousy or to the fact that (for instance) he hates how bro closed a big legal deal while he, himself, didn't get a year-end bonus....well, husband still needs to be civil for YOUR sake. Do you think you can approach him to do it, for you and for the sake of modeling good relations for any kids involved?

OP, I agree with others that you should confront DH. However, in addition, make sure you aren't inadvertently adding fuel to the fire by comparing your DH to your brother. Make sure he understands that you are not "keeping score" between the two of them.

Call your DH out on his jealously of your brother. Tell him he needs to be respectful around your brother. If DH can't manage his feelings and be civil around your brother, then go visit your brother by yourself.

Have you talked to him? "Honey, your cracks about my brother are kind of getting to me. I feel like we can't be around him anymore. Can you tone it down?"

DH and my brother used to get along great when they were in their 20s, and I loved that they were friends. In their 30s, not so much. My brother has had a very successful career and made a lot of money. DH is a little bit of a "keeping up with the Joneses" type but has had only middling financial success. All of a sudden he hates my brother, doesn't want to be around him, makes snide comments about how my brother had everything handed to him and doesn't work that hard (not true -worked his way through law school, works crazy hours at Big Law firm).

DH is generally pretty competitive about work, but this is way worse than I've seen him with anyone else. It's to the point where I don't want them to even get together anymore because DH's behavior is just ugly. I'd rather just get together with my brother when DH isn't around, which is very awkward bc then he asks why DH never wants to hang out anymore. How do I fix this?