it is likely you will need to replace everything within the opening.

Identify the header and measure the size you need. Often when replacing just doors, the whole thing isn't sealed from the weather properly, and is often not the same thickness.

Best to start fresh and examine everything, maybe the sill is bad and needs to be looked at.

For peace of mind, a new start is often the best course.

Who will be doing the work? Best to discuss with them and let them measure so they have responsibility.

You do not have a large overhang and double doors are inherent leakers. I would rip the entire thing out and use a 42" door with 24" sidelites.

What you have is a twin-door with sidelites, which is one unit.

If everything is in good shape, i.e., doors, weather stripping, threshold, etc., it can be done 3 ways. 1. You can modify existing doors by cutting out raised panels in whatever configuration you like and ordering glass inserts.

2. Order (2) new doors with glass, you can have them come with pre-mortise hinges matching existing, and with pre-bored locks matching existing locations. 3. Replace the entire door with sidelites.

Depending on your budget and the condition of your existing door, option 1 would be the best and cheapest way to go.

Here are a few configurations you can make to give you an idea

Good lick

Another vote for a single door and wider sidelites.

I happen to like double doors if you have the space and new ones are made to not leak air. I do however think the whole unit should be ordered together and that will also give you the ability to choose the glass together with the side lights and door to look cohesive . But in this cse I think a wider single door with wider sidelights will look a lot better in the space you have

Maybe narrow down the door‘s style and then consider if your sidelights will suit. Money might be well spent though to ensure a seamless effect. Have a company or two provide quotes and be sure they do the measuring.