The Househusband eh... *Mode Shift engaging*
So he washes all their clothes...lovely. So how does he know who's new piece of lingerie belongs to who? :3
I don't know enough about Klarissa's and Natasha's personalities so I'll leave it to you.
But as far as scenarios go, he can be involved in at least one thing during their individual days. Can be something mundane that they do together or important. For Chifuyu, just the act of drinking together would be something, or all of them going to a bar. Maya loves sunbathing (whimsical thought) so she loves having Ichika rub the sun screen on her. Natasha likes having him for a home workout partner so she can tease him with what she wears (or doesn't wear). Klarissa is into cosplay so she likes to dress up in different outfits and tries to get Ichika into some as well. Tabane is just touchy-feely with Ichika all the time since he's the only guy she ever sees.
Or they can have some sort of weekly competition between them to see who gets Ichika's Service over the weekend. By Service I mean the full gauntlet of getting a massage from him after their bath, having him feed them at dinner in front of everyone; something like that.