I think that I probably already know the answer to my own question, but I thought that I would throw it out here just in case I am wrong.
My question is:
1) Do people in this situation special-order a one-piece window unit that is already made up of two side-by-side double hung windows in one unit?; or,
2) Should I just buy two same-size double-hung windows and just frame it out so that the center post between the two windows built by me (us), and then just mount each window in its own pre-framed space?
My guess is that the standard answer is "2", not "1", but I decided to ask anyway.
And, of course, any other thoughts, suggestions, or considerations regarding this project would be welcomed.