Do my wife and I both need to show 20,000 THB for a visa on arrival in Thailand and what are the requirements for our return ticket?

Hi and thanks in advance for your advise. I was told that I have to show 20.000,- THB (equivalent?) and a return ticket applying for a visa on arrival. I'm a German citizen and married. Wife is German too.

Question one. Do both of us have to show 20.000,- each?

Question two. We will get a 30 days stay permit but might want to extend another 30 days. What validity of our return ticket will be accepted in this case by customs?

Thanks you