Starting May 15, 2018, it will be possible to create a Nintendo Account Family Group via your Nintendo Account settings. One Nintendo Account can create a family group and up to 7 other Nintendo Account holders can join it; all members of the group will have access to Nintendo Switch Online family membership.
Just as Nintendo stated recently, the Family Group option is now available for your Nintendo Account. Here's some tidbits about the new option.

to invite someone to a Family Group, all you need is their email address
that other person does need their own Nintendo Account,
select someone to be the group's admin (by default, it's the person who created the group)
you can also remove members (something only the admin can do)
child accounts cannot be removed you can have up to 8 people in your group, including the Admin and any associated Child Accounts
Child Accounts created before May 15th are automatically added to your Family Group
you cannot be part of more than one Family Group, at least not with the same account
anyone that's part of the Family Group can subscribe to the Family Membership
when someone subscribes to the Family Membership, everyone else in the group automatically benefits from it
set specified members as Guardian (for Parental Controls)
only members who are at least 18 years old can become one
members of a Family Group do not share Nintendo eShop funds, purchase history, or My Nintendo Points
when a member becomes a Gu...