Your inheritance will have come from somewhere, get whoever paid it to you to write a letter stating the provenance. I'd also be prepared to show how you will be able to support yourself for the duration of the DTV 570k baht isn't going to keep you
rather than cancelling a DTV will any of them do the conversion to another visa type as per the original DTV official announcement? Just wondering why anyone would want to cancel rather just convert?
A new year will make absolutely zero difference. I would say you will be allowed to enter providing you have no other history but will only be allowed a 7 day extension at most. Best to have a ticket out of Thailand, 20k baht in cash and accommodation booked. If you do have history in Thailand all bets are off
You each need your own money, your own paperwork, your own everything. There are a number of consulates that don't require the money to have been in the account for any particular length of time, even though they ask for 3 months of statements it's the closing balance of the 3rd month that's important
The money must be in a personal account. Money in a business account belongs to the business and not you personally. They want to see 3 months of bank statements but only the final month needs to have the 500k baht showing. The problem you have is waiting for the statement to show that which might be the end of the month if that's when your bank generates statements