ASM Chart for synchronous system
You'd need four states: "Lift empty", "1 person in lift", "2 persons in lift", "3 persons in lift".

Every time the ENTER signal becomes activated, the state machine has to switch to the next higher state, since one more person is in the lift. (Except when it is in the "3 persons" state because there's no higher state, but nobody will enter the lift when the alarm is sounding anyway)

Every time the EXIT signal is activated, the state machine has to switch to the next lower state, except when it already is in the "empty" state of course.

If none (or both) of the signals are activated, the state machine has to stay in the same state.

If the state machine is in any state except for the "empty" state, it should activate a "LIGHT" output. If it is in the "3 persons" state, it should activate an "ALARM" output as well.