I have 2 for versatility but usually leave them in the same position. I think 2 opens the space a bit more but that could be because I choose black for my TV room.

How would you inside mount a single headrail?

Two will give you blinds that function better. How much light control depends a bit on whether there will be drapes. Probably nice to give some light control if not.

I would do just one shade, as long as you have enough room to inside mount. I've been happy with Hunter Douglas products in 2 houses and they have a narrow cellular for tighter spaces. A single shade will block more light because you won't get the light leaking in the center section. I will be using all TD/BU again in my new house.

@Liz H what do you mean when you say "opens the space a bit more?"

Maybe two shades will make the window and room seem taller?

@suedonim75 the divide between the two window is set back a bit, so I think there is available room. I will double check to make sure. I believe that @Liz H has two shades on a single headrail.

One shade. Would be a pain to adjust two shades, trying to get them even.

You really think they will open the window for ventilation? I doubt it with what looks

like a lanai/porch on the other side.

I have 2 headrails but they are so close together they might as well be 1.

I’ve been opening all my shades evenly for years. Its not a difficult task. And why would a porch keep them from opening their windows? The OP specifically mentions opening the windows.

Sorry, I didn’t answer the other question: I guess it’s because I have black blinds, the white window pane makes them look less oppressive. I do have a large blind over a double window in my office and I wish I had bought 2 separate blinds. My office has light grey— I do not like the large size.

@suedonim75 I was wondering too about @Angel 18432 comment about her doubt anyone would open the window for ventilation because the window is in a porch or lanai. Actually, the roof in the photo is a second story deck. Perhaps @Angel 18432 was expressing doubt about guests opening the wiindow for ventilation because of security concerns, given that the window is located on the ground floor level.

Yes, I thought it was ground level. I see a swing, so that's what steered me that way.