Here's what I've got!

For Aldous: Mathias Beaumont is an UCPB Slytherin who was two (?) years below him at school. Albert Pettigrew is 29 years old but works at the Ministry and is also an UCPB so that's an option.

For Balt: STAY TUNED, I have Benjamin Ross, Ross' (slightly) younger brother coming soon who might work. Otherwise all I'd have to offer would be Finnian and getting stuck with Finnian is eveyone's worst nightmare.

For Ezra: Cornelius Sherington III was a Gryffindor in his year. UCHB and nobility, but not notably haughty in his circle of ~magical~ friends? Finnian Byrne was also in Gryffindor a year above him. Albert Pettigrew was in his year and Slytherin but exceedingly less likely to make friends with him.

wellll I'm mostly useless, sorry girl :P