If you want "unlimited" hot water for all 7 all the time then tankless. If you have the right location and want to save money, energy and have better indoor air quality then choose a better tank water heater, as in a Heat Pump Water Heater.
I have a client who's very happy with the AO Smith Voltex 80 gallon unit and they seem well reviewed. My choice would be Steibel Eltron's 80 gallon unit.
6 people would push the performance of these two beast's ~80 gallon first hour rating, but if you could stagger usage well and put up with running out of hot water from time to time, they would definitely be a better investment.
Q
Thx
Q