How can my wife apply as a dependent on my Non-OA visa renewal, and what are the financial requirements for both of us?

So you two got the "second year" from Non-OA visas already and it is ending in coming February, correct?

Q. How can my wife can come under me as dependent instead of each of us having to supply the financial requirements for two different individuals.?

-> An easy answer is, no, she cannot be a dependent directly from her Non-OA entry.

As a rule, you have to apply for the first 1-year extension for the same reason as the initial visa. In your case, as you two have Non-OA for each, you two have to apply for a 1-year extension based on being over 50 (starting with Non-OA). Then you might be able to change the reason for the next 1-year extension or later.

If your wife wants to be dependent on you, she has to leave Thailand to get a Non-O dependent at the embassy/consulate in another country.

Q. Do I have to do the 800,000 baht deposit for each person?

-> Yes. As a US passport holder, you cannot get an embassy affidavit for your financial proof. You have to show funds in a Thai bank account. If you want to use your funds in US, you have to consider applying for a new Non-OA in US again.

Q. This would require my wife opening her own bank account?

-> Yes, in case you two apply for an extension from Non-OA entry for each. Or you can check the local immigration office if they accept a joint account, then change your current one to a joint account if the answer is yes.