I'm following the same route.
My wife was my dependent on my retirement visa. To do the same again I am told that we must get a visa before entering Thailand. This visa can (maybe) have my wife as dependant but it seems this visa will be a non-OA and will need medical insurance. Difficult at my age.
Doing a visa conversion from a visa free entry, or a tourist visa, in country and you can not have your wife as a dependent. You have to get a retirement visa each, I.e. you both have the 800,000 baht in the bank on the day of applying for a conversion to a non-O visa. And your wife must transfer the money from her account to her sole account in Thailand . No joint accounts.
I'm ok for myself as I have the 800K in my account. Appears my wife will have to transfer to her account in Thailand, luckily we had opened such an account before covid.
I might be wrong but I have been following things for the last year.
One thing has changed. If you enter on a visa free 30 day entry and you must get to immigration with 21 days remaining that is a rush. But immigration will give you a 30 day extension on your visa free entry, so you have 38 days to sort things things out and still apply with 21 days left on your stay.