Dot would be very interested in them thinking they're cool and older, probably would follow them around like a duckling if Qiu or Tamarack isn't there. I think somewhat of Baxter's indulgent(?) behavior is the reason why Dot follows him, and because of Ren's aversion to girls- that's what made Dot follow Ren (Because I was a child that wanted to be everybody's friend). She wanted to join when Qiu offered but since Tamarack didn't, and she didn't want Tamarack to be odd one out, she refused, but then joins after the two bonding moments.
Shù does not like them because she's intimidated by them. They didn't want to refuse Qiu's offer, but the thought of having to be in a club with two strangers- older strangers nonetheless- scared him, a lot. Honestly, with how timid they are, I feel like Baxter and Ren would feel pity and a bit of annoyance with Shù.
Cran doesn't like Baxter because something about that boy doesn't sit right with him, he's a bit more iffy with Ren, he doesn't like the way Ren treats Tamarack, but he's chill with Ren, for the most part. He joins in the club because why not? There's not much else in a sleepy town.
Fran is iffy with Baxter because Baxter pointed out the birthmark on their forehead- the birthmark also has a scar over it and the origins is a sore subject- and with Ren, they're teasing the heck out of them to see the reactions. Fran is also in the boys' club, probably bonds with Baxter over ragebating other people. (Baxter feels like a person to ragebait)
Ari hates them- Baxter feels like 'rich boy 101' and Ren is too huffy for his taste (Look who's talking, Ari 😒). He's not in the club at all because why would he want to do something so childish? Very much saying it to their faces, and probably insults them in French.
Hee-Jin admires Baxter greatly because he's mature and rich (rich people facinate her like how some people are facinated with birds), heavily dislikes Ren because of the 'not liking girls' part of Ren's personality in Step 1. Naturally she doesn't join because of that and I think Ren and Hee-Jin have a rivalry and bicker- most of the time ending with 'Why am I even bothering arguing with a little kid?' From Ren.
Phya sees Baxter like a cat and that amuses him greatly, it would probably clock his crush on Qiu. He feels for Ren and probably herds Tamarack away to keep Ren comfortable, if the dynamics were set, Phya to Ren would be: Teamworking, Praising, and Doting. I think it does it's best to help Ren out if the group has to make contact with girls. He's in the boys club after the 1st bonding moment.