As you can see in the image, there are three routes (digital nomad, soft power, and being related to someone else with a DTV. These are all listed under #5 purpose of the visit, but required documents 1-4 are required by all regardless of purpose of trip. So everyone has to supply 1, 2, 3, 4, and 5 (5 depending on the mode you are apply via)
My understanding (could be wrong), is that immigration can only transfer visas that they have the ability to also issue for you here in country. Since DTV is visa that is only issued outside of Thailand via a consulate (MoFA), Dept. of Immigration in Thailand can’t transfer this particular type of visa, like it can with others. I still think it is somewhat speculation though.
They also might ask for you to supply all pages in your passport (happened to someone recently). If they see you are back in Thailand, you would be denied. Better to just stay there until it is issued.
Yes, he would have to apply for the visa outside of Thailand. Same process, but instead of showing medical appointments or remote work, he will need to show that he is married to you and that you have a DTV. Same requirements though regarding visa costs and having 500K in the bank.