It is relatively easy to play any kind of harmonic with both hands simultaneously, thus forming a two-note interval within the normal range of the harmonics.
The left hand can produce 2 or 3 harmonics simultaneously on different strings, provided that the harmonics are of the same kind (octave, fifth, etc.). The right hand, however, can only comfortably produce a single harmonic. This is due to the different hand positions of the left and right hands while producing harmonics.
By combining the hands, it is therefore possible to produce four harmonics at the same time.
Four harmonics played with two hands.