Harbrace 9b: Capitalize titles of persons that precede the name but not those that follow it.
Governor Ann Richards, Captain Machado, Uncle Verne
Ann, Richards, the governor; Machado, our captain; Verne, my uncle
Words denoting family relationships are usually capitalized when serving as substitutes for proper nouns:
Tell Mother I'll write soon. [Compare: My mother wants me to write.]
The AP stylebook agrees with capitalizing titles before names but tells us to lower case job descriptions. That's why it's Coach Bobby Knight but centerfielder Mookie Wilson.
(Yes, according to my old Sports Illustrated stylebook in its black ring binder, the position is written as one word, "centerfielder," but the area is written as two words, "center field." Oh, yes, and although positions in the field are lower cased, the coach at a position isn't, as in Third Base Coach Don Zimmer.)