yes, a friend of mine is processing an ext based on being over 50. He told me they have asked for documents more online with a Thai wife visa, like photos outside the house, crazy, its these exception that make the process so unpredictable
The rule is 2 months before the submission, some offices ask for it addtinally to k
Be kept for the 30 day consideration period. Prachinburi for extension for a Thai wife asked me to keep 2 months before 3 months after. Its worth checking locally.
Some offices require documentation from your pension provider, its best to check with your immigration office, also all payments should be recorded as international payments in your bank book
If your child has a Thai birth certificate and your named on it. You could get an visa extension based on supporting them. There is one benefit that is you only need to have 400KTHB on the date of the application, rather than 2 months before for a Thai wife, even so your still need marriage certificate etc. Also check with where be living some immigration offices have their own requirements