Which type of visa

We are a family of four, 2 adults and 2 children all with separate UK passports. We are travelling to Vietnam and Cambodia. We arrive Da Nang on 30.03.2018, staying 7 nights then fly to Cambodia on the 06.04.2018. We arrive back to Vietnam on the 10.04.2018 staying 5 nights before flying back to London on 15.08.2018. I understand with our first 7 night stay we would not need a visa being UK passport holders but for our 2nd visit would we need single entry or multiple entry visa to re-enter Vietnam ?