You might consider a long sided swag valance (usually with one center valance per window) but with extra valances pieces between the two side pieces. If you sew, you might be able to make that from what you already have on one rod and just cover the side frames of the window group and wall beside it, leaving most or all of the glass exposed. Basic mini blinds hung within the window frames would, when pulled all the way up, be hid by the valance and they'd enable you to still control light and privacy as needed.

https://www.touchofclass.com/hellina-long-swag-valance-pair-80-x-63/p/R491-006/?kc=IMFPFS2&code=IMF08&color=White&size=80%20x%2063&tid=IMFPLA&gclid=EAIaIQobChMI7pKLrafW8AIVWTizAB3BYQreEAQYAyABEgKToPD_BwE

The 18" would be the length. Depth would be the projection from the wall out to the room.

You don't say how long the current valances are or give a measurement of the wall and the window, so impossible to say what the length should be. The length depends on those measurements, not whether it's a home setting or not. Also, the bottom should come down further. You should not be seeing the top of the windows like that. Valances shouldn't be just sitting on top.

Yes, you can hang a valance only on the bay.

Thank you for commenting. I thought the pictures would be enough. I can give the window measurements a bit later. When you say "the valences shouldn't be just sitting on top", do you mean that they should come down over the top part of the window, not just the decorative frame? That's what I'm planning to do, with the 18" length.

Also, do you mean that a valence plus drape panels on the the long window and valence only, on the bay window, would be an acceptable treatment?

Even though the treatments will be different, make sure all rods are hung at the same height; do panels on the the windows, and valances on the bay windows with the same fabric.

I think you could simplify the look by using the box valance over the corner windows, and then just the drapery panels on the smaller windows, without the valance. They don't need to be the same. You might also consider taking all your valances down and keeping the windows bare for awhile to see if you get used to a cleaner look. You have a nice view and really don't need anything there at all.

you have nice windows and a great view, why do you want a valance?

I should have explained that I'm removing the entire window treatment that you see in the pictures. I'm redecorating the entire room - new furniture, paint and window treatment. I'm want a simpler, less fussy look, so that's why I want the box pleat valence over the windows. It would look too bare and unfinished without anything, in my opinion. The green draperies etc. that you see in the pictures will be completely gone.

Everything will be hung at the same height. The windows go up to slightly under the crown molding. I hadn't thought about valences on the bay window and just panels on the tall window. It's an interesting thought. What does everyone think of that?

Well, I like it a lot and that’s why I suggested going in that direction. If you want to cover the top of the screen, you need a certain length valance. With rods hung at the same height, that length valance would cover too much of the other window glass.

A good read:

https://prioritywindowvalances.com/how-far-down-should-a-window-valance-hang/