Yes, put a single wide piece between the windows.

In our home we have 3 1/2” casing.

What does your casing look like? Is it a simple rectangular profile?

This is it. Also comes in a 2 7/8” only sizes available per our sales rep for this design.

What's the plan for these windows as they seem to be up against the ceiling with no room for trim.

Multiple ways to do this.

You could also do this, using a custom trim between the windows.

PPF- Wow that looks great! Thank you for the mock up. You bring up a good point about those upper windows and I could not tell ya- yikes! I’ll be meeting with carpenter tomorrow.

What do you recommend for baseboard trim? Do a lower profile? And roughly what are the measurements in that custom casing you did on the surround?
Thanks so much!

And roughly what are the measurements in that custom casing you did on the surround?

I modeled your trim profile quickly, so the overall size is what you show above, but the notch and stepped down part are close, but not accurate. Also, the space between the windows is less than what you show.

Thank you!!