Summer tiki y viable?

Celica is pretty useful, if you need her a neutral iv is not too bad and can definitely serve you well

For Leo honestly it doesn't really matter what ivs you get, his pretty useless regardless. It would take quite a lot of investment to make him viable for much of anything

New tiki is fantastic, built in breath so she doesn't have any of the normal downsides of being a flying dragon. She might honestly be meta changing, and shes super fast so the +spd iv is very useful, you could even go an offensive dragon build on her

Celica has good IVs since Neutral=Good
Leo.... not so much since his weapon refine need him to have high def and that IV throws it out of the window. But you could go for Bladetome build for potential 1 shot capability or Owl tome.

Summer young Tiki.. Yes, though not the best bane but she has the best Boon since she is the fastest dragon right now you could build her with a player phase build. or stick with enemy phase and with that spd she will prevent double attacks really easily.

you can build them but if you think that they are not good for you then make them learn their default kit and wait for a better IV.

I disagree with some of what the others have said. That Leo isn't especially good with his prf but he'll use a raven tome well and he comes with QR for an iceberg. I wonder if you can get away without TA? Since he has atk boon. Then even the CA units get busted.

+spd -def is good, arguably even optimal, depending on how you want her to play. Which bane was she going to take? res? Makes sense if you want to play her without DC, maybe, but it's getting thin against Nowi, who she cannot expect to OHKO. HP bane is likely worse because she doesn't have much to begin with and at her kind of speed it's mixed bulk. She doesn't have a weapon refine, either. I think the analysts who wrote her character page missed more than a little in recommending an HP bane. If you play F.Grima you know that this kind of stat spread is not monstrously tanky, especially without fortify or ward fliers. She's very often fine for one opponent; if they targeted the weaker defensive stat (res usually), you might not have enough HP left to take another hit. F.Grima is better off dropping her res and trying to avoid mages (though she'll generally handle one no problem as long as it's not Reinhardt or a Naga tome), trying to tank using her def if she needs to tank multiple hits. Flying Tiki doesn't have this privilege because she needs to fight dragons (which also rules out the atk bane in my opinion, otherwise I would have considered it more due to flier buffs), so it's between def and HP. -HP makes things a bit thin against blue dragons; -def means she's not as good if she gets hit by multiple physical attacks. Def can be boosted using buffs; HP cannot.