You may be looking at the tuning "backwards". Dulcimer tunings these days are specified from the Bass to the Melody string and we only ever mention the doubled melody string(s) if they are actually tuned differently.
The Bass string is D, your A string is the Middle drone, and the d string(s) are the Melody string(s) an octave higher than the Bass.
On a 26-27" VSL, a 14 ga should be easily tuned to the 5th above the Bass string -- A. Fret the Bass string at the 4th fret, and sound the note -- that's what you tune the Middle Drone string to -- A. Your Melody strings should be a bit lighter gauge -- 12s. Tune them to d an octave above the Bass string D.
BTW -- Bagpipe Tuning is defined as a Bass string tuned D (for example) and all the other strings tuned an octave above -- Ddd for example, not DAd. DAd is the Mixolydian Modal tuning.
updated by @ken-hulme: 04/27/18 06:07:14PM