Condolences, sounds like your agent has it under control.
I switched to the guardian visa after a divorce, I submitted to Phuket each year;
The divorce agreement we registered at the local district office, a new copy every year even though it has never changed.
The usual copies of the passport pages with your extensions back to the original O visa, and 2 photos
The child's birth certificate. I also gave them a letter from the school which probably is not necessary.
The bank letter and statement which has to agree with your bank book. I transferred the B400K a week before.
3 pictures, only problem I had was the lad was topless in his bathers beside the pool in one photo, did not accept that, but did not ask for a replacement. I normally had 3 photos, one inside the house and 2 outside, one with the house number in the background.
I found the volunteers in Phuket very friendly and helpful, the Thai processing my application the first year called me a cheap Charlie for not going to the B800K retirement visa. Later years I had a woman who was more friendly even when I got the wrong divorce document one year.
I have one question my lad goes off to university overseas next year and will still monetary need support, does that qualify? I am guessing if he is not in Thailand it will not, so started the B65K a month retirement after last years visa was issued just in case.