Happiness is not determined by the level of the Pokemon - happiness has it's own system on the Pokemon. The happiness meter on a Pokemon is unseen, and is between 0 and 255. 0 being the lowest amount of happiness, and 255 being the highest. Depending on your game, a list of ways to increase your happiness is presented in this link.
For those Pokemon to evolve via happiness, it only needs 220 happiness. But the highest possible happiness is 255.
Hope I helped. :) Source: Above Link
