@Li *****
Yes they could use the O Spouse Visa. However, it has to be renewed every year with all of the paper work and Immigration visit to your home. It costs 1900 Baht a year and you have to collect all the documentation from bank etc. If you need to travel you need to pay for re-entry permits. The DTV is 10k for 5 years and no re-entry permits required. No need for annual renewals. For many the DTV may be more convenient than a O Spouse