I have a friend who's an American citizen living in HK with 2 half Thai children. He wants to move here, and understands all the processes he needs to go through but needs to know if the 2 month seeding requirement (for a Non O) for the 400,000 is flexible or can be arranged by an agent. Does anyone know someone who can help or has had any experience with this in the past. Any help is much appreciated. 

Is he the legal father of his children by way of marriage or legitimization of their parenthood . That is a requirement to apply for the extension of stay at immigration.

For an application based upon being the parent of a Thai there is no amount of time for the 400k baht to be in the bank. It only has to be in the bank on the day he applies.