This is actually a really interesting question if you consider the dynamics at play. Realistically, at the time, there was no "neutral". Neutral was Switzerland, not in that it was choosing not to fight, but in that it is not in Britain. So, this is my characters, disregarding neutral as an option.
Selwyn
Wouldn't join the Order because what are the chances they would trust him? He could flee to Germany but that would draw attention and put his parents in danger. So he'd just keep his head down and hope for the best.
Monroe, Shylock & Destrey
Okay, so in that political climate, their parents are probably not publicising why they're studying blood purity.
I can see Monroe masterminding some scheme where they pass themselves off as pureblood supremecists, and their parents' studies as an attempt to prove the superiority of purebloods. So they wouldn't have taken a side but they might have publically supported the Death Eaters as a form of self preservation.
Angelique
Would have joined the Death Eaters for kicks. Obviously.
Tifanie
Would be living in France.
Ariane
Would have joined Dumbledore's Army.
Malaika
Would join Dumbledore's Army
Jenna & Calixta
Are second gen canons so their attitudes are influenced by their parents being in the first war.
If I ignore that, Jenna would have joined Dumbledore's Army but refused to fight and Calixta would probably be naive enough to try to join the DA and get cursed either by them, or by the other Slytherins for "betraying" their house.