Vietnam with teenagers

Welcome to the forum oldmidwife. I'm not sure 27 counts as a "teenager" but it would help to know the interests of you and your travel companions, what time of year you will be there, how you want to get around (public transit/drive/fly), and what you have planned to do already.

Does “eight days” include the days you are flying?

Are they 17 or 27? Is 27 a typo? How many nights on the ground?

Have you found any guidebooks to buy ior borrow from a library? Perusing them will give you a starting point. Have the 17 or 27 year olds made some input about their likes or expectations? Some more info would make it easier to give advice. Your question is very broad.

With the Mekong Delta and one beach destination.
When will that happen?