Hola Carlos,
Although I am not absolutely certain (my flying in Nicaragua these days is solely as an airline passenger/ my professional flying takes me to the Middle East), I believe the Atlantic Airlines fleet in Nicaragua is currently 3 Let 410's. They certainly have more deployed under Guatemalan, Honduran and Costa Rican registration and I believe they move these around as necessary, simply reregistering them as the need dictates.
According to the TACA Regional website, La Costeņa has 2 Shorts 360's and 4 Cessna Grand Caravans.
Those are the 2 airlines in Nicaragua, now that Aerosegovia is gone (although the aircraft were still on the ramp at MNMG as of a few weeks ago).