Who should I promote to 5 star

It really depends on how these units are going to be used. Fir should not be promoted as she really needs her Res to tank mages/dragons. A neutral Tiki is kinda worthless. An +Atk Eliwood looks nice, pair that with Blazing Dundral and he should do a ton of damage and trigger specials much quicker.

So 3 reds or a blue. Do you need another red? Or do you need the blue? 2 (Fir & Eliwood) are more magic tank type of units. Do you need this type? Even then, Fir should retain her Res and would be better with a -HP, defense bane instead.

Adult Tiki has neutral IVs, I would look for a more optimal IV, like +Attack - HP, or + Defense -HP or +Res -HP. You should ONLY take a -speed bane if you are not aiming to play competitively (aka arena/ arena assault). You can always promote her and merge into a better IV later as well. If you are doing a 1 time promote and not interested in merging at 5* +10, then I would wait for a better IV. If you are going to one day +10 her, then definitely fine to do the neutral one.

Male Kana - he just requires more investment. He will need Lightning Breath+ (From Adult Tiki / Nowi) to be better optimized, or have Distant Counter in the A slot. He is more limited on merges due to being a Grand Hero Battle reward - but still a reasonable option to build if one wants.

Edit: Male Kana will be a bonus unit in 2 weeks, so unless you have your Askr trio at 5*, then he should be more strongly considered as well. The Askr trio member will score higher though if they are built (and if they aren't, perhaps they should be considered instead of the 4 you listed...)