Visa and Entry Stamp Process

I have a few questions about the visa process.
We and our daughter’s family, ( total- 5 adults + 3 children ) are taking an Asian cruise on Norwegian Cruise Lines. We will be visiting four cities in Vietnam 18 March - 23 March 2019.
1. Can I complete and pay for all 8 of the visas myself?
2. I would like to know your costs per person and total? Will I still need to pay additional for the stamps to someone on arrival?
3. Because we will getting on and off of the cruise ship at four different cities, is the one month single entry the right visa to get?
4. This is my biggest question. The various web sites states that we would get the actual visa stamp at the airport. Since we won’t be arriving into Vietnam at an airport, is there a procedure to pay for a and get the visas when we dock in Hanoi?

Thank you for your help.
Al Lundberg
bigallundberg@comcast.net