Garcia and Kieboom should only be kept in Rochester if Dave Martinez refuses to play them every day.
No reason to send Robles down. He isn't going to learn anything new after 1,100 MLB plate appearances.
Robles has been over-powered by major league pitching. That's no place to learn to hit. Send him down to AAA where he can compete before pulling him back to the majors. He looks miserable, both in his swings and dribbling grounds, and in his expressions. Looks sadder and more nervous even than Erick Fedde does when Fedde faces a tough hitter.
Years ago, I read "Moneyball". In it, Billy Beane tells the story of his signing as a many-tooled prospect just after Strawberry, the twin superstars-to-be who were expected to save the Mets. One spring, Beane met Len Dykstra, a no-tools prospect who sneered at Steve Carlton: "That guy's got nothing". Dykstra was confident to the point of arrogance, even though he had none of the "tools" that Strawberry and Beane, or even Mookie Wilson had.
Robles seems to have no confidence. Maybe he will never have Dykstra-confidence, but he won't gain or regain it being overwhelmed. Give him a chance in AAA.