And sure, they could be fixed. But look at them -- they're nothing special. The big windows in the big house, I'm not replacing those; they're fabulous. But these? There's just no reason to work hard to keep them.
And fortunately, Pella makes vinyl inserts for existing wooden frame double-hung windows. You remove the sash (or, as with this window, you buy it preremoved), and stick the new window into the hole, shim it, screw it down, and caulk it. It takes about an hour, according to the brochure.
So. The bedroom window is 36"x54". Standard, $166. These two are 30"x54", which is not standard, but as you can see, there's just window frame between the two of them. There is a 32"x54" standard window. I'm just going to put a board between two of those for the front window here, after removing the intermediate framing post there. I forget the exact price of the 32"x54" insert. The other three (hallway, kitchen, and bathroom) are all 28.5"x54", which neatly fits the standard 28"x54" given a little quarter-inch board on each side. I believe those cost $116 per. So we're talking about maybe $800 and two days' work to replace all the windows here in the carriage house.
That is hereby the plan.