The gods of Teleria really are with you if you have these champs allready at the start of the game.
All three of them can do more than just give some healing. Apothecary gives a speedbuff, Skytouched can remove and block debuffs and Shirimani has some crowd control with her AoE freeze. They all are worth lvl 60.
You just need a champ for AoE def debuff in addition to them and Kael and you have a team for most dungeons. Apo - champ for def debuff - Kael - Shirimani could also work as arena team.
I'd probably put my vote on Shirimani but you gotta prepare yourself as she will require a lot more resources to ascend, book, etc, than Apothecary. I also wouldn't prioritize Skytouched for now if you're just starting out, she's a really solid champ but will be helpful much later in the game.
Shirimani is good for arena and faction wars and if you have nothing better then dungeons too. I would go Apoth first as his speed and turn meter boost is very very usful and his heal is top notch too, also a multi hitter on A1 so will help you wirh fire knight progression right up to and including 20.