Now you can really appreciate why I suggested to assemble and finish the interior of these bays before installation to the dollhouse. They are tiny. You might not have this same problem with the one inch scale version of this dollhouse.
I decided to stain my bays to match the staircase and floors since they are too tiny to wallpaper. After staining and painted the window mullions inside and out using the same technique that I used on the dollhouse shell windows.
After that was dry, I began installing the trims.
Not only are the bays tiny but you have to cut out your windows from the window sheets. Use the trim as a guide for the side windows and the actual window openings for the front ones. Make sure you leave enough leeway at the edges so the windows can be glued onto the dollhouse.
The side windows have square shaped trim but the front windows trim has to be assembled from the four wood trims provided. This would have been very hard to do with the bays installed.
Install the side trims first for your front window and then the top and bottom.
It's going to be messy. The parts are very small and even if you are using a fine tip for your glue, it is still going to get everywhere. Don't panic. Tacky glue dries clear. Just don't get any on your window panes because then it will be visible, even being clear.
Once the glue dries, you will see that everything begins looking nice and neat and detailed.