This may be an odd question, but are there are any generally accepted or used terms when describing a gathering of races. 

If City A was filled with Orcs, Bugbears, Minatours, I don't know what I'd call that grouping (besides Monsters, but I'm trying to think of another term)

If City B was filled with elves,gnomes, humans, I'm not even sure what to a term to describe them as besides something like "civilized race"

Any thoughts? 

Polite terms, or slang?  For polite terms, I'd go with not mentioning it but implying that people are aware of the difference (if they weren't, the two towns wouldn't be divided like that). 

For slang A: monsters, uglies, brutes, anything that could refer to jocks in our world    B: faeries, pretty boys, shorties for some, anything that would refer to nerds in our world

Thinking more about Polite Terms.  

There aren't standard terms. If a city was generally filled with Orcs, it would be described as Orcish. Goblinoid. Minotauran. If it was a mix of races I imagine you would use the same sort of terminology you would use here. Cosmopolitan, multicultural, diverse. But if you're trying to get across the idea of civilisation, you'd do that easily enough with your description of the settlement itself, rather than the occupants.

I’d suggest one of two options:

What you’re describing struck me as a little like Warcraft with two factions (horde and alliance), it might be an easy shorthand to just use faction names

In the real world we tend to group people by geographical location, usually despite coming from different ethnic/cultural backgrounds. I grew up in Wigan, (northwest England). Most people from the town were generally happy to be called ‘Pie eaters’. People from Liverpool were ‘scousers’, from Manchester ‘Mancunians’ (or ‘Mancs’). I’m pretty certain that I got into an argument with a scouser (we were drunk and it was friendly really) that we both thought that the other should be properly called a ‘Woolly back’/‘sheep shagger’ (like I say we were drunk). 

I think if you have a town of different creatures, you’d just lump them together ‘Oh great, the Cauldron Stealers are here!’ (Meaning the Orcs & Minotaurs from Stinking Bridge have turned up and as everyone knows Stinking Bridge is famous because it’s where Dagdha the Witch had her cauldron stolen).

or something

Pillars of Eternity introduced a term I've found myself using elsewhere that speaks to at least some of this.  That being "Kith" - a term used to describe anyone who claims membership in the 'civilized' races of the world.  Humans, dwarves, elves, aumaua, orlans, godlike (sort of) - all considered kith races.

In D&D, the Kith could be considered all those races who primarily interact peacefully, through trade and cohabitation.  The PHB races, primarily.  Non-kith would be those races who're isolationist and rarely interact with the broader world, such as gith or aarakocra, or those races whose primary interaction with Kith races is raiding and eating them, a'la orcs or goblins.  There's no corresponding "not kith" term, but one could be produced out of a hat if the idea appeals to you.  The main differentiator is that any member of a non-kith species, whether that individual is sapient and peaceful or otherwise, is generally met with suspicion at best and outright hostility at worst, because only kith are known to be...well, not baby-eating raider monsters.

For funbunnies, a DM could change what does and does not count as a kith race between campaigns, and let all those jackweasels who keep trying to insist on playing monster-race characters that sure, they can...but a non-kith character will face severe hardships in any kith territory.