Do I need to prove the 500K THB financial requirement when entering Thailand on a DTV visa?

You have a multi-entry tourist visa. Any tourist can be selected for secondary screening on arrival. The requirements are 20k baht in cash, the first night's accommodation booking, and an onward/return flight within your initial allowed period of stay(180 days). In reality, hardly anybody gets asked. When acquiring the visa, there was no requirement to keep a balance of 500k after it was issued. If you attempt to apply for an in-country 6-month extension, then you will be required to show the funds again, along with all your other documents - and more :D

When you applied for the visa did they ask you for any money proof? I’m applying for our visas as a family tomorrow , I’m super confused of expectations as online says so many conflicting things.

Maybe, maybe not. But have 20k in pocket

The 500k is a visa requirement, you had it when you applied for the visa so theoretically you should still have it. It's the proof of funds which shows that you can support yourself during the 180 days stay. So you should be able to show it each time you are entering Thailand in case you get pilled aside for questioning

I highly doubt it, they may ask to see that you have funds in your bank account, you show something reasonable for your plan of stay on that entry

It all depends on how you physically look, act, and present yourself when they first see you, then by your history on the computer