It is indeed possible to play 2 artificial harmonics simultaneously, but it is very difficult.The fingers I and M are used for the harmonics and P and A are used to pluck the strings respectively. If you are using +12 fret harmonics (i.e. an octave), then this technique is only feasible if the LH finger on the higher-pitched string is even to, or more towards the bridge then the lower-pitched string. For instance, LH 1st finger on 5th string 3rd fret (C), and LH 3rd finger on 2nd string 5th fret (E), then the harmonic points would be at the 15th and 17th fret respectively. This is certainly do-able, but not of much practical use.
Assuming +12 fret harmonics still (fretted string length divided by 2 if you prefer), it's probably impossible to use this technique if, for example, LH 3 is on 5th string 3rd fret C, and LH 1 finger is on 2nd string 1st fret C, since the higher-pitched string fingering is more towards the nut and that would put the RH fingering into an extremely contorted position. However, since there are about 11 usable harmonic points along the length of every string (including fretted notes
), it's theoretically possible to use these kind of LH fingerings as well, although its use seems dubious at best.