hi anon sorry i took 3 months to reply i didn't want to think. unfortunately i still don't want to think so this answer will be short sorry

(vaguely in order)
ichisaki: some time during middle school/main story because saki wants to check it off her list of things to do and ichika is hopelessly in love
honasaki: probably the first to kiss after whenever they confess. sakis like ok we're dating i get to kiss you now and honami is the one who lets her do it (side note i think honashiho would be disappointed but not surprised to know that ichisaki kissed in middle school LMAO)
shihosaki: almost definitely after honasaki
ichihona: a few days after they start dating honami absentmindedly leans over and kisses ichika and ichikas like ?!,@?#(@#,@(@, and honamis like oh sorry ive wanted to do that for a while it kinda came naturally. ichika blushes a lot
honashiho: honami asks nicely and shiho lets her do it
ichishiho: would take them forever tbh but i think ichika would be doing one of her patented Gay Monologues TM and shihos like i can't not kiss her

also im posting a fic vaguely related to this for polyneed week so look out for that ❤️ ok bye

😭😭😭 no see if they made parallel harmonies about "ichisaki have never disagreed in their life and spiral the second they do" i would've been happy with that bc we see ichika always always trying to make saki happy and caving to her demands (which hnsh also do but icsk have the added context of middle school) so to have them be at odds would be weird for them and open up a new side of their relationship. i was joking about "my girl is mad at me hope i die" but i seriously think they could've pulled it off but Nope its focused on the creative differences rather than the conflict itself. there could've even been a parallel (ha) between honashiho having to work out their differences from the very beginning since their reconciliation but ichisaki not having experience with that and struggling with it. shrugs