The DTV is for online work only, you need to demonstrate work that is done online while in Thailand. I submitted a portfolio which highlights the work/tasks to be done online.
An updated bank statement of 500K THB seasoned for a minimum of 30 days must be submitted when applying for a 6-month extension at an immigration office.
Regarding sponsorship you need to ask first who they approve as sponsors. Some embassies only approve of employers sponsoring. Location doc - utility bill, lease agreement etc. ChatGPT very useful for a sponsor letter.
He will need to get his DTV first if you want to apply as a DTV spouse. It is ok to put down a hotel. A letter of employment from the company is needed detailing permission to work remotely in Thailand. Submitting paystubs and highlighting their deposit on a bank statement will be of great benefit.