Castillo, a former Texas Rangers farmhand who spent the last year in the San Francisco Giants organization, is the only one whose signing had not been previously reported.
Originally signed out of the Dominican Republic by the Rangers, Castillo is 33-37 with a 4.63 ERA in 251 minor league games (37 starts) in his career. Last year, he was a combined 6-7 with a 5.34 ERA in 37 games (seven starts) at Double-A and Triple-A.
Marrero, a 25-year-old first-round pick of the Washington Nationals in 2006, has hit .232 in 133 plate appearances in parts of two seasons in the major leagues.
Paul, 28, is a 2003 fourth-round pick of the Los Angeles Dodgers who has hit .254 with a .316 on-base percentage in parts of five seasons with the Dodgers and Cincinnati Reds.
De Jesus Jr., 26, is a 2005 second-round pick of the Dodgers. Primarily a second baseman who can also play third base and shortstop, he has batted .205 in 80 plate appearances in the majors in parts of two seasons for the Dodgers and Boston Red Sox.