An old door from pre-1978 probably was painted with lead paint. I don't think there's process of glass "shedding lead". Old bathtubs leaching lead into the hot water, the vintage drinking glasses your mother gave you might leach lead into your drink, lead in non-food grade glazes on plates and bowls leach lead into your food, old metal window blinds shed lead dust when they are operated, heavily used old painted surfaces creates airborne lead dust... yes. Glass... no. Especially a 60's house when lead was only added to glass to make fine crystal. Very unlikely it even has lead.

Do you need a double door? Whay not do a anice single door with one sidelight. I think a 24" exterior door is really too narrow to use by itself .

Pictures would help. If there is an over hang you "could" open the opening up for double doors but I do not care for double doors, especially if there is no substantial overhang, and even then not a fan. I would most likely go for a single door and sidelites. BUT pictures would tell the story about which would look better.

Yeah, don't know about lead that sheds. But regardless if that's true or not, the best solution is to keep the frame intact and replace the tiny double doors with a 36" wide single door with narrow sidelite on the latch side.

THe current double door will not meet modern egress codes. A single larger door is required, at a minimum. The cost to make a large 72" double door, that is not all that functional, will be really large.

What does shedding lead mean?

If glass is your only issue, you can call a glass company to replace the glass.

If you want new doors, you can consider a 36” single door with an 12” single sidelight. 24” is too tiny, like bathroom doors. Most average appliances and furniture can make it through a 36” door. There are times the door has to be removed, but not often, so take weight into consideration.

I found a door/sidelight combination I like for my house at doortodoorco.com. I wanted a large single sidelight and they have lots of sizes. They said they could make a custom jamb kit.

For a long-lasting solution, I would suggest replacing the door with the current measurement. I had my door custom and it was not very expensive. I also had my patio door installed with a screen door to prevent my main door from aging easily.