Generally speaking, Jubilost is one of those characters that doesn't require any multiclassing to be effective throughout the game. Alchemist scales pretty well from beginning to end.
As far as Kalikke and Kanerah, that's a bit more complicated. Early on I'd picked the sister that fit my game thematically and mostly just ignored the other one. Later I realized that I was missing out on a resource. Here's an example:
Good-aligned party.
Protagonist: Aldori Swordlord - Rogue / Sword Saint / Duelist - Offtank / Melee Damage
Octavia: Standard Build - Buffer / Ranged Damage (Skill stacked for Stealth/Perception/Trickery for traps)
Linzi: Iron Halfling Build - Tank / Buffer (Skill stacked similar to Octavia as backup in case of low roll)
Tristian: Mystic Theurge Build - AoE Healer / AoE Nukes
Ekundayo: Standard Build - Ranged Damage / Kite Bosses to trivialize game
Kalikke: Standard Build - Ranged Damage / Spot Heals
Now, the problem with Kanerah was that she didn't really out DPS anyone else and I almost never called her up. As you can see, there are no real holes in my party. She'd just inadvertently show up whenever I'd left Kalikke too exposed. Finally, I realized that she was better as a gap-filler. I reset her back to basics and had her take Wizard levels. This meant that at early levels, she'd show up, buff everyone with Bull's Strength, Enlarge Person, Haste, etc. and then switch out immediately, allowing Octavia to focus more on damaging spells. Later on the Communal Protection spells, Animal Growth, Summon Monsters, etc.
This worked pretty damn well and later I started experimenting with making them even more niche. Like when Kalikke was the off character, making her the ultimate spelunker. Everything into Perception and Trickery and stacking all related feats and class bonuses. As a character she was worthless on her own, but in terms of opening every God-tier lock and passing every impossible Perception check she was the perfect stand-by.
Later on I fiddled with having Kanerah go Wizard and Kalikke go Cleric and both be summoning focused. On tough fights they'd both blow their loads with max-feat'd summons, switching back and forth when one spell level was tapped and moving down to the next. It was fun, and it worked a lot better than any solo-summoner I'd played, but summons are just... meh-tier in this game.
Anyhow, the end-game with Kalikke and Kanerah, as I saw them, was in picking builds that enhance your party. Which is ultimately why I quit solo-builds and started on my ill-fated party builds.