You should be able to build it how it is .

i like double Hungs with a station above or below so you don't impede the walkway when they are open. Could do a 3 lite slider with grids.

I like DHs there like todd mentioned.

Thanks for the suggestions! From my understanding that would increase the space between windows and not keep the same silhouette of 9. Right now it's a 2×6 between in white.

My concern with the double hung is my dog jumping through them when they are that low to the ground.

If you put a stationary above or below each double hung you would have nine. You can lower the top sash only to vent. The spacing a will change depending on the profile of the window you choose. The Windows should be ordered as 1 unit mulled together to keep the spacing minimal.

If you like the silhouette of what you have why not just go back that way. Can do stack mulls of 7 fixed windows and 2 awnings just like it is. No reason to reinvent the wheel. To save on cost you could also do do the lower sections in 1 larger picture window with an SDL to divide up the look or some manufacturers have simulated meeting rails which is a larger SDl to give it that divided look.