Compilation:
  g++ -c point.cpp
  g++ -c tripple.cpp
  g++ point.o tripple.o main.cpp

I have added 'Include Guards' in the two header files.

point.h includes tripple.h
tripple.h includes point.h
class Point is forward declared in tripple.h
class Tripple is forward declared in point.h

A cpp file includes its header file - should always happen.
  Thus: point.cpp includes point.h
        tripple.cpp includes tripple.h

main.cpp includes both point.h and tripple.h

This is a nice and symmetric solution - as I see it.