Julie, the passage you quote makes it clear that the "glasses" are the windows, but breeds further questions.

First the glasses (ignoring the blinds for the moment):
I take it that when the glass is down it has been lowered into the body of the door and the window is open. The footman is instructed to put the glasses "further up", implying that the windows are generally kept open when the carriage is not in use - but why? Because the glasses are easily broken? To prevent the interior of the carriage becoming stale and musty? When the family enter the carriage they expect the windows to be partly open. Do I have that right?

Now the blinds:
Presumably these hang from the top of the window aperture, inside the glasses. They are put down when the carriage is about to be used, so when the door is closed the carriage would be dark inside - how odd! Why would that be the preferred way of doing things?

Also why, when it rains, are the blinds not to be put down until the family are just going to get in? Is it to preserve the blinds from being damaged by rain entering through the partly open windows? If so, it would seem more helpful to instruct the footman to keep the glasses up (closed), so that rain could not come in and make the seats wet.

It is all very confusing. I am probably being obtuse or missing something vital (my wits?). Sitting in a Regency carriage for thirty seconds would undoubtedly make it all clear.

Does this question more properly belong at L&T?