How do you share one subscription with your family?
You take one paid plan and share it with up to six accounts: you plus five others. The storage is shared, everyone's library stays private.
The main thing to understand: the storage space is shared, your library is not. Everyone on the plan has their own account with their own photos and videos, and paying along does not give anyone access to the others' images. If you want to share something with the group, you deliberately create an album for it.
It works for a family or a couple, but also for a group of friends splitting the cost. On your own it works too: then you have a roomy, ad-free archive for yourself. You can always add people later.
See the plans to pick the storage that fits your group, or read one plan, shared with up to 6 accounts first. How you then share an album with the group is in sharing an album with family and friends.