If you need to do so, you may wish to use more than one instantiation of Pianoteq, but assign each part to received different midi channels. Then you will need to either split your keyboard to send two independent channels, or use two keyboards.
Regarding 4' and/or 2' pitch, one needs only to set your keyboard to input +12 and/or +24 midi notes.
In the case of harpsichord models, should one wish to invoke a lute stop, you might try increasing the soundboard's impedance, such that it will dissipate the sound more quickly. Just be sure to assign this changed model to yet a different midi channel, unless you wish to perform the entire piece with the same lute stop.
Cheers,
Joe