Anyone walking into a crowded room might scan them en masse, but they will identify with nobody.
It's a general melee and a back-drop to a scene. The people populating that crowd are like extras milling around the screen in a television show. They will be forgotten a second later.
If you want your original characters to blend effortlessly into your fan fiction, then they can't all appear at once. There's no empathy for a mob here nor anywhere.
Your great storyline might demand it though, so some preparation is clearly necessary.
Allow for several paragraphs, if not whole chapters, where your readers are led by the hand into meeting all of these newcomers. Your canon character will need to be in some situation where people arrive, singly or in small groups, to be gradually drawn into the narrative. A party is good; or an interview process.
Bear in mind that the more people being introduced, the less likely it is that they will individually stick in your reader's mind.
I once had thirteen significant original characters to insert into a fan fiction. It took me about a third of the novel to maneuver the majority into the cast.
First I had two main canon people looking at an internet forum. They encountered three of the OCs there and discussed them. My readers met them through the eyes of familiar protagonists, which served as the aforementioned introduction.
Next my canon characters visited a launch party, attended by the three newcomers. By now, those reading could fix them as acquaintances and position them in the world of this story. I was able to use this setting to sneak in a couple of other OCs. They stayed on the outskirts of the narrative, until the canon people could draw them in.
Thereafter, each time the group met, another person could be added to the encounter. The others were alluded to in conversation, which meant that it wasn't a shock when they turned up. Never, at any time, did I allow any of them to run away with the storyline. The main characters were always the focus around which the supporting cast orbited.
By moving a mention into a meeting, then an acquaintance into a familiar face, my readers were gradually able to recognize the new names. After a while, they could even empathize and identify with them.
It took until the very last act before the final OC turned up. He had been talked about throughout, so the reaction was unanimously one of welcome. By the end of the novel, I had a much wider scope for story-telling, than the restrictive world bequeathed to me by the canon's author.