You don't need 8 people to form a Family Group, 8 is just the maximum number of people that can be inside a Family Group...People wait for up to 8 strangers is because they want to save a few dollars...if 7 people pay the Family Admin $8 each, the Admin get the Nintendo Switch Online for free and still got change to buy a meal...
It is US$19.99/year if you were to sign up for Nintendo Switch Online alone...If you sign up for the Family Group, it is US$34.99...So long as two person sign up for the Family Group, each person is paying lesser than if they were to sign up alone...
Edit: Want to add the following link so that people can be aware before deciding to sign up with strangers...
https://www.reddit.com/r/NintendoSw...getting_nintendo_switch_online_be_careful_if/