I think only Luffy will learn Haki!
As I was pondering about their (haki related)abilities, I've come to conclusion that Oda probably wants to show us how people learn haki. And he will use the crew for that objective.
Take for example:
Zoro, we'll probably learn MAD sword skillz.
but because he's learning from mihawk, he probably won't learn haki.
Mihawk, has never dealt haki slashes, but he does have his swordsmanship to keep him on par with the rest.
And it would be wonderful for zoro to learn haki in one piece part 2, because you would really then see what is necessary to learn haki colours. "plus" it's a strength that can be obtained by training it, so he could have something to grow on(strength-wise).