12 years is ridiculously optimistic. Here’s this months VB, you can see the current date on it for that category is April 2007, so 16.5 years ago. https://travel.state.gov/content/travel/en/legal/visa-law0/visa-bulletin/2024/visa-bulletin-for-october-2023.html
But it’s not linear, that category doesn’t move much so don’t expect it to advance quickly - @Boiler said the other day that it’s only moved forward 1 month in the past 3 years. You can see all previous VB’s on the website to give you an idea. So at that rate you’re looking at a heck of a lot longer than 16.5 years, which is why you shouldn’t expect anything before 20 years or even far, far longer. Then add on the time it will take for your brother to sponsor his children and that’s potentially another decade or two - more if any of them are married by then and he he has to become a citizen first.