When a person who filed a petition (US citizen) needs to expedite the case, the reasons for expedite are based on hardship falling on the US citizen. For example, US citizen falling ill, unable to work / provide care for themselves = reason for expedite. Petitioned alien relative under the same circumstances would not be a reason for an expedite.
Ultimately USCIS would grant an expedite if bringing over an alien relative would alleviate some sort of burden on the US citizen. Not the other way around.
HOWEVER
There was recently a case here of someone being granted an expedite for their Russian fiancée who was cutoff from being supported by her American fiancé due to sanctions. According to USCIS rules his request was not supposed to be approved.
Now your situation is entirely different because your brother is under a completely different category of visa priority, and not an immediate relative (as per USCIS definition). But I'm just pointing out that some rules don't seem to apply these days when it comes to Ukraine / Russia specifically.
With that said, I think Uniting for Ukraine is your best (and probably quickest) path forward.