I assume you are applying for an annual extension of stay based on having 12 months of minimum 65k baht transfers from overseas each month? The letter needs to pull out those transfers and show them line by line. You'll also need 12 months of bank statements and to update your bank book on the day you apply.

You can't switch inside the country, and most places want you apply for a Non-B outside of Thailand in any case as it requires a lot less paperwork

What your husband will have is a medical certificate from the hospital which he can use to apply for an extension of stay based on medical grounds, not for a visa. These are normally for instances where the patient is unable to travel so immigration might not issue the extension if that's not obviously the case. The fact they want him to go to another hospital might be a clue they're not happy with the certificate. That certificate also won't help with a DTV application, you will need a treatment plan for a minimum of 6 months from the hospital signed off by a recognised doctor on official stamped paperwork

@Rio *****

no idea what that means

You are legally obliged to file a 90 day report every time you spend 90 consecutive days inside Thailand

@Yam ******

you can go and do one now and pay the fine, or you can wait until you next interact with an immigration office and pay it then

Every time you spend 90 consecutive days inside Thailand you are legally required to do a 90 day report. The consequences of not doing one is a 2000 baht fine the next time you interact with an immigration office. The fine increases to 5000 baht if you're arrested and found not to have done one.

This is all very confused. You have a 60 day tourist visa which you can extend one time for 30 days then you have to leave. This is not a multiple entry visa. You might be able to get a medical extension via the hospital but this is normally due to you being unable to travel. You should have applied for the Multiple Entry Tourist Visa (METV) if you want to be able to come and go, with this visa every time you enter during the 6 months it's valid for you get stamped in for 60 days (although you don't have to stay 60 days). There is also a specific Medical Treatment Non-O visa that allows you to enter for 90 days and which can be extended inside Thailand, that you can also get re-entry permits on.

@Ken *******

she can get the Non-O inside Thailand but she requires a bank account and to transfer 800k baht into it from overseas before she can apply. It's currently pretty difficult to open a bank account on a tourist entry

If she's not yet left home get the Non-O visa inside her home country, makes opening a bank account much easier once she arrives