What are the financial requirements for a 1-year extension of stay as a couple on Non-Immigrant O visas in Thailand?

It's very unusual for a spouse to get a Non-Imm-O dependent visa on top of the married partner’s own Non-Imm-O Retirement Visa.

If your wife really does have a Non-Imm-O as your “following spouse”, she has no financial requirements to meet.

However, now I am not sure how you proceed further:

For the application to the 1-year extension of the stay permit on Immigration, you need to prove your marriage.

You would need your original marriage documents translated and legalized by the Royal Thai embassy in your home country.

In Thailand - AFAIK -

you need these documents legalized by your embassy in Bangkok , and co-legalized by the MfA (again, I am not 100% sure about the correct proceeding)

The spouse applying as a dependent generally does not need to meet the retirement financial requirements themselves. The primary applicant acts as the sponsor, You must provide a marriage certificate that is legalized/authenticated (translated into Thai and certified by the Thai Ministry of Foreign Affairs) - I suspect you already have this since your already obtained the Visa with dependant. Best to visit immigration office and ask them directly just to be sure.

They are taking advantage of retirees with the overly complicated Visa system. If you have a joint bank account (Ideally Thai Bank account), putting 1.2million baht will meet the financial extension requirements for both of you, or 400,000 individually for her and 800,000 in an individual account for you.

I think the poster has a Non-OA visa

So you both have non-o visa, where did you receive these visas?

Almost no embassy will give a non-o 90 days based on being over 50.

Then issue a non-o 90 day based on dependant of the over 50 non-o.

This needs to be clear or you may be up for a surprise when you try and extend.

If this is correct then the primary is only repsonsible for the finances, based on proof of dependant- marriage in most cases.

Did you're spouse prove finances on the original application or just the primary finances?

My, also Dutch, wife got a retirement visa when I still had my business visum. After I sold my restaurant & company, I went as depended on her retirement visum. We where officially married in Thailand at the Amphur and the Thai marriage certificate was sufficient for the immigration. The 800.000 guaranty from my wife was accepted for both of us.

My husband has a non-oa, I have a dependent non-o and so does my daughter. It's off of his income, but I'm pretty sure she cannot be a dependent based off of a non-o. It will have to be a non-oa.

Retirement visa holder only but you will need a certified copy & translation along with your original marriage certificate

It's pretty unusual for a spouse to get a Non-O dependant visa these days, particularly at the same time as the Non-O retirement visa holder. But if your wife does have a Non-O as your dependant she has no financial requirements to meet. Only you need to meet the financial requirements