From the top:
-Ichi is, of course, with his two friends from elementary school who went to the private school he failed to get into, who first appeared in a flashback in chapter 42 and also came up in chapters 55-57.
-That's Chii in the middle, who we also know went to Ichi's elementary school from chapter 56. The two girls with her are from a one-shot Norio Sakurai wrote way back in 2015 that also featured Chii called 半開さん-"Hanbira-san," title written in english as "with her eyes half open!" I don't believe any scan/translation of this exists online, just a couple of photos floating around the internet.
-The girl on the left with her hair in a big bun *might* be Moe? The mouth has what looks like the same distinctive shape and the end page of chapter 8 suggests that Moe didn't go to the same elementary school as Yamada, so she might have gone to Ichi's.
And for Yamada's:
-On the far left mostly obscured by one of Yamada's friends is Kanoya, and the one with her whose back is to the camera is Nyaa, who we've seen with that bleached short hair before in a flashback way back in chapter 17 ( https://mangadex.org/chapter/707076/13 ).
-The blonde girl with Yamada is probably the same girl she briefly goes off to talk to in chapter 58 ( https://mangadex.org/chapter/1105254/3 ). Her other friend might also be the other one there, but the resemblance isn't quite as strong.
-And finally, the three guys on the right in Yamada's picture are from the omake chapter at the end of volume 4, which hasn't had a proper translation yet but will hopefully get one here eventually. They run into fifth-year Ichi and his two friends who had just gotten packs of cards for some game and the black-haired guy was about to just steal a rare one before Ichi stepped in and antagonized them. He was just about to get his shit kicked in until the blonde one stopped his friend because there were three girls walking by, who turn out to be Yamada and two of her friends, and he didn't want to be seen doing that in front of them. In that omake they claim to be a year ahead of Ichi and friends but obviously that doesn't track with them being at the same graduation as Yamada- I suppose it's possible that it's just the mohawk guy who's graduating and the other two are just there for their friend? Additionally, people suspected when the v4 omake went up that the blonde member of the trio was a younger Pickup-pai, due to his slight resemblance to him (just change his hair style and you're close enough) and because in that omake the black-haired guy was wearing the same kind of hat as his friend from chapter 53 ( https://mangadex.org/chapter/1029113/2 ).