Recommender's affiliation
I think it matters much less than you think. A recommender speaks for your past work and for your future potential. The specific field is less important than that they respect you for both aspects. The other elements of your application will show your basic suitability, such as courses taken and such. But the recommenders need to assure the admissions committee that you are serious and hard working as well as adaptable and creative. The specific field matters less. 

Their specific field isn't all that they know. People who specialize in some field also know some things about the requirements of other related fields. So, the examples you cite seem less important than what they will say about you. 

A good letter from a person, in a related field, who is widely known and respected, can be a very positive thing. 

But even a recommendation from a Language professor can be positive (wildly different field) if it supports your suitability for study and making progress. "This person can really think and write" is a good thing to have said about you. (Don't take this as a suggestion that all your letters should be from "wildly different fields", of course)