Dragonite - power up or evovle?

I'd get the Level 24 defender to Level 30 for better gym placement. Rest is already pretty good. Having too many things to power up in paralllel is a bit of a headache, especially when the candy is rare (although it may not be so rare for you?).

Power up all the defenders, ignore the attackers which are pretty good enough.

So, i think it is very relative... Dragonite is a good defender, it's undeniable... But it is also one of the most effective attackers in the game. I'd rather spend the candies in one of the two Defenders, or both, maybe, cuz they have better IVs and one of them is pretty low now.
BTW, it is good to start thinking of evolve this dratini and to gether more candies to power up it, cuzit will rock with any moveset, hahaha.
I think you should analyse what are you in need now, if you need more atking or defending pokes at the moment.

I would max the lvl 30 71% ivs one and keep the dratini for the future. The defenders are pretty good too, we all know Snorlaxes and Laprases are better but unless you have Snorlaxes/Laprases enough to put on gyms and dont need more defenders, Dragonite still a beast: top tier, greatest stats and CP to sit at the top and you got two of them with 90%+ ivs.