You will need to get your Non-O visas from outside of Thailand if you do not already have a Thai bank account that can be funded to meet the financial requirements (unless your Embassy still does the income affidavit)
If he is under 50 them the retirement Non-O is not an option but married to a Thai or father to a half-Thai child are his options but the paperwork is greater
You need to pick the correct Purpose of Visit - in your case Pensioner staying no more than 90 days (where it states Visit Thai Family here) - you selected Non-OA long term stay
Is same sex marriage recognised by Immigration now? I thought it was only some Embassies and Brandon was referring to foreign wife/Thai husband marriages.
You will need a ticket to enter Thailand, one to leave within 60 days then another ticket entering Thailand when applying for your METV as proof that you need one