@Steve1580 – I just got up to speed by actually reading this whole thread.
If I understand correctly, you have a room with about 20'×15' listening space. It has built-in bookshelves that have at least two shelves. The lower shelf is 16" deep × 16" high × 30" wide and the upper shelf is 16" deep × 30" high × 30" wide. I saw the attached picture of one of the shelves. What that photo doesn't show is how the shelves are placed in the room.
From that photo, I can see one of the shelves in which you might place a speaker, but I don't understand how you would use speakers mounted on stands. Where would the stands go? And why are floorstanding speakers not suitable? They have a similar footprint to speaker stands.
I agree with TLS Guy when he said "Putting speakers inside shelves can be problematic." It is important that the speakers be located so that the tweeter, or a point mid-way between the woofer and tweeter, is at a similar height to the listeners' faces (or ears) while they are seated. In bookshelves, it is also important that any speaker be placed such that its front panel (often called the 'front baffle' in speaker building) be at the front edge of the bookshelves, or even protruding a bit. Finally, if the speaker cabinet has a port tube, it would be better to locate the tube on the front baffle instead of at the rear of the cabinet. If a cabinet design shows a rear mounted tube, it can be relocated on front as long as the cabinet width and interior volume are unchanged. It may make the cabinet taller or deeper than in the original plans.
For any speaker with multiple drivers in one cabinet, it is important for acoustic reasons that the cabinet sit vertical and not sideways. Each driver should be arranged above or below the other drivers. Work with your wife on questions of cabinet finish, appearance, and general location, but do not compromise on the vertical alignment or the height above the floor of the speaker cabinets.
If you can fit a speaker cabinet that is 8" wide × 18.5" tall × 12" deep, you might consider building pair of the
Zaph Audio ZA5.3 MTM speaker kits available through Madisound.
Cabinet plans are included at that web site. MTM speakers, with two mid-woofers, will do better in a room of your size.
Somewhere in your posts, you mentioned using hardwood in your build. For speaker cabinets solid hardwood should be avoided. Instead, use MDF or good quality plywood such as Baltic birch. You can finish those cabinets with any veneer or paint you wish.