No. Only way somebody else can check your reservation is if that person knew your name, flight number and the reservation code. Even then, they would not know if you boarded the flight. No airline will give out the passenger list of a given flight.
Subsequently, do airlines keep passenger records?
In the air travel industry, airlines keep a record of their passengers in what they call a PNR, a “passenger name record.” It could include the passenger’s itinerary, fare details, how the passenger paid, any special services required, age, and sometimes gender, too.
Simply so, how do I know if a passenger has checked in?
An airline won’t tell you if a person has checked in or not. If you know their confirmation number, you can go to the airline website and try to check in for them and you can find out that way. If you don’t know any of the information though, you should mind your own business.