True the student is a member of the flight crew and is not a passenger.
However, if the instructor has not completed at least 3 take-off and landings in the past 90 days (almost 3 months!!!!) then one would have to question their ability to both safely operate the aircraft should the sutdent be unable to do so and also correctly demonstrate all the required parts of the sylabus which includes various take-offs and landings.
If you find that all your students at at the stage where they do the take-off and landings on each flight then your training organisation should provide the posibility for you to retain the required currency either by scheduling you to fly with students at an earlier stage or taking an aircraft and completing some circuits with another instructor.
I would regard 90 days as being a very extreme limit when dealing with members of the public.