@Nicolas **********
, (editted) what you uploaded is the requirements list for a short-term extension based on Clause 24, visiting Thai family for 60 days. This extension can be applied only once per visa/visa-exempt. And this doesn't require proof of funds of 400K baht.
If you want to apply for a long-term, 1-year extension based on being a family member of a Thai national, you need a requirements list for clause 18. This requires proof of funds.