シングルビザかマルチビザか?

I want to apply for a visa but I don\’t know if I need a single or multiple entry 30 day visa. We fly Melbourne to HCMC and stay for 1 week then go down the Mekong delta to Cambodia for 1 week. Then we fly from Siem Reap to HCMC (3 hour stopover at HCMC) then fly home to Melbourne. We will not leave the international airport and plan to be in transit there (& will not leave the international airport). We will just collect our bags and re-check them in as it\’s a different airline to go to Australia and stay in transit). So do you think we just need a 30 day single entry visa. Do you agree as with the second trip to Vietnam is just a stopover ? Please let me know so I put in an application for the 6 of us travelling together.

ありがとう