Well that would give you 26 all up.
But I think it pre mixes the tracks first to a stereo file for the Drum and for the Medley track so ram shouldn't be an issue.
In the MultiDrum window you adjust the volume first, not sure how the Medley would work with "Play All Simultaneously" without a volume offset ?
This works with WinBB
Biab Win More Audio & Midi Tracks and gives better mix control with vol/pan/FX for each track, but I haven't found one yet for MacBB.
There should be ReWire in BB18.