Dragon team ?

Adult Tiki is incredibly good when it comes to tanking, as long as you've got a bit of investment. I think any way you look at it, she'd be a slightly better pick than Garon at the moment... Out of curiosity, what are Adult Tiki's IVs?

Tiki and Nowi are both incredibly helpful as they have built in DC. If you have a good IV for one of them, go ahead and promote tat one. Since you already have L!Tiki (blue) maybe lean towards Adult Tiki. Even if you don't have good IV's, Tiki, Nowi, and Fae are all worth +10 merging, so there is nothing wasted in promoting one to start a merge project.

For IV's, +Res/-Spd is strongly perferred for Tiki. Nowi is more flexible with boon, but you really want to find a -HP Nowi because she makes use of all her other stats, and the refine fixes the HP bane. +Def/-HP is the best IV for a well rounded Fae.

Depends on how you want them to play out, Corrin isn't the best when it comes do LB/DC because of her low Res, but she can be a very good Falchion counter with SwordBreaker, Even tho Corrin is bad with LB/DC I still use LB when I have DD for her seal and it works decently. You can also run her with her base DB and be a good debuffer, all in all Corrin is a good speedy physical tank and good Falchion counter with
Dark or Water Breath (spd or def refin)
Steady breath
SwordBreaker
Close Defense seal