What are the requirements for renewing or extending an O visa in Thailand, and can an affidavit be obtained from a solicitor?

The husband, holding a multiple-entry O visa, can renew or extend it without needing a Thai bank account with funds if the extension is based on being married to a visa holder. In cases where he must meet financial criteria (like being over 50), he would need to show either 800K baht in his own account or verify a monthly income of 65K baht with a notarized letter from the embassy. It is possible to use a joint bank account if it meets the documented requirements (balance of 1.6 million baht if using the joint account for a retirement extension). For obtaining a signed affidavit, he must go to the consulate for notarization; it cannot be done by a solicitor in Thailand.