I am planning to install replacement windows like this on my porch. These windows look to be about 3" apart. Is it possible to do vinyl siding between these windows when they are this close together?
Depends on what you want and if you are going for a trimmed out window or running the siding and J channel tight to the window. If it were mine I think I would trim it all out with PVC lumber.
It will be a tight squeeze. What I would do is take a bit of scrap J channel and siding and cut some short lengths nail them to a scrap piece of 2x6 and give it a try.
I'm not an expert on siding but have done some on my place. My front porch had a couple strips like that and i filled them with strips of white flashing the same stuff they wrapped my old wood windows in. It looks ok.
I would go the route that Bud described in his first reply. It will look cleaner and make the window units look like one unit. Putting in J-channel is going to fill most of the space between the windows. I wouldn't even do that narrow of a piece of siding with fiber cement siding let alone vinyl.
We have two sets of double hung that are 4" apart, similar to your photo
Between is a strip of 4" wide wood, along the lines of what Bud mentioned in #2, above. (Only ours is wood. If I had to do it over, I'd use what Bud suggested.) The sides & top are cased with brick mold. (Sills are sand stone)
Paul