Convincing Jewel cichlids to spawn again

I've got three jewel cichlids, two of which I've had nearly a year and are
in the rather big and ugly phase of life, one who's a bit smaller and newer
that I got back in the winter. The first two have spawned three times, but
the only one with surviving fry was last october, they did it twice more a
couple times apart but the eggs/fry must have been eaten, and they haven't
spawned since. Are they past breeding age? Are they too used to each
other? Is there anything I can do to revive the romance between the two of
them, or one of them and the third? They don't do much anymore other than
lurk in corners... :-( Better food? Temperature change? Vacation?