If memory serves I would say they react to him with disdain. The guy who people think is the MC's possible grandfather and that other guy have no interest in talking to him. They lie about not taking a trip this year when he wants to be invited and then when he leaves talk about doing it in like two months.
Doesn't Jade talk about Stephen making money from selling stocks? Wouldn't say the market is anathema to old money.
The two men in the front hallway definitely didn't want him involved in their trip, so that might be disdain. The two students in the back room just thought he might have drunk a bit much. I guess it could go either way.
As for the market, I usually associate it with new money. The money was 'new' because someone had just made it, so business, finance or investment were the usual mechanisms. Old money came from owning huge tracts of lands, ideally with the ability to rent them to those who would do the actual work (or tax the lands directly, if the family was nobility).
The categories change over time, though, and the world in BaDIK may look at it differently. But I just found it interesting that Rusty, who is definitively old money, was rejected by Tybalt in the flashback.
It could be because Rusty managed to push nearly all of Tybalt's buttons (and might have got all of them if Tybalt saw him hit on Jill). But it might also indicate that the Preps are more about new money than it first looked. Yes, Jill is there, but she is considered an exception, and we know Tybalt has an interest in her.