Vietnam Visa On Arrival Queries

Hello,

Can I please confirm the followings?

1. For the stamping fee of USD $25 to pay at the airport, is it cash only or can we make payment with credit card?
2. Does the On Arrival Form have to be filled out before arriving at the airport?

3. Can one group of people fill out one on On Arrival Form or does each person have to do one individually?
Please let me know and thank you for your help.