What documents do I need to apply for a DTV visa in Thailand while working remotely for a UK company?

As to the letter it should give you permission to work remotely from Thailand and confirm that you will have no interaction with Thai entities or clients inside Thailand

Your husband won't want a DTV, he'll need to wait for the company to sort out his Non-B visa. For you if you want to work remotely from Thailand you need the DTV based on workation to legally work. If the company you work for is big enough and you earn enough you could also look at the LTR Remote Worker visa which is one of the best visas available but the bar is quite high. These are the only 2 visas that allow you to work remotely from inside Thailand

It is quite straight forward to get a DTV as you have everything required. Upload your contract and evidence of your work if you have some collate into one PDF using merge on ilovepdf.com and condense if the file is too large to upload. It's free. Put a cover note explaining what you have collated and a nice note about why you want to come to Thailand. Then add 3 months bank statements showing your savings again a little note explaining - collate and compress if needed. Be careful to fill everything on the form with no mistakes double che k everything, one typo and your application will be cancelled and you have to apply and pay again. It's easy but just check the detail. You'll be fine. Hanoi is quite quick I've heard.

He cannot work without a visa so why do you need a DTV, won't 60 days visa exempt be enough?