As many as a dozen deals could be made in the coming days.
The Marlins have tripled their international budget from a year ago. Team owner Jeffrey Loria and the front office have made the international market, primarily Latin America, a priority in bringing in young talent.
"Jeffrey made a decision to increase the international signing budget to give us an opportunity to acquire premium guys," general manager Dan Jennings said.
If the organization was operating with budgets from previous years, it likely wouldn't have been able to land any of these five players.
Marcell Ozuna, signed out of the Dominican Republic in 2008, is one of their homegrown international players.
The pure tools of Castro, Capellan and Villalobo have the Marlins elated that they've lured in future impact stars.
After officially signing, most of the players will start off at the Marlins academy in the Dominican Republic as they get introduced to professional baseball.
From the 2013 class, left-handed-hitting outfielder Isael Soto, who is just 17, is now playing for the Gulf Coast League Marlins in Jupiter, Fla.
The Marlins note that Miami is the Gateway to the Americas, and the organization needs a strong presence in Latin America. They view the July 2 signing period as potentially as significant as the First-Year Player Draft to bring in young talent.
Albert Gonzalez, the Marlins' director of international operations, and his staff have been extremely active, putting together what the club feels could be a top international signing class.
Capellan, 16, is a 6-foot-4, 185-pound outfielder. The Marlins don't announce financial terms, but Capellan has agreed to a $500,000 bonus.
Castro, 16, is a 6-foot-3, 185-pounder considered a five-tool player. His bonus is around $650,000. Castro's raw talent resembles a young Vladimir Guerrero.
Villalobo, 16, is a switch-hitter, and a speedy shortstop who could project either at short or second base.