Q: My iMac doesn't read DVDs

Have you used a cleaning CD in the optical drive?

Sounds like it is time to replace the optical drive then

For a replacement, try https://eshop.macsales.com/shop/optical-drives/superdrives/

Also, could try powering down and unplugging your iMac and take a credit card completely covered in a microfibre cloth and stick it into the CD slot and then pull it out and see if any dirt comes out and onto the cloth.

Wipe the loose dirt off of the cloth and reinsert the cloth into the CD/DVD slot, again, clearing the dust and dirt off of the microfibre cloth each time before reinserting the cloth/credit card until no more dust/dirt/lint comes out of the CD/DVD slot and no more dust/dirt/lint appears on the microfibre cloth.

Then try a DVD again.

If you have access to the other iMacs, i.e. connected somehow, you should be able to share their optical drive:

Use the CD or DVD drive from another computer with your Mac - Apple Support

It should.  Set the System/Sharing preferences on the Mac with the working optical drive to what's shown in this screenshot:

and then follow that document and give it a try.

it should work. There are sites showing how to disassemble Macs for replacement of various parts.  See what you can find to guide you thu the process.