icloud plan

You can share it with any or all of the family members. Assuming that you are the organizer, you get to invite the individual members to share the storage. As far as I know, you can include or exclude whoever you want in the family. In addition, each member can decline to accept and continue to use their own plan if they choose to do so.

If you are already sharing a smaller account with family members, an increased account will also be shared with them. Assuming you don't just want the larger account for yourself, you'd need to remove those from family sharing that you didn't want to share your account.

Only the family organizer can set up the shared storage plan so what you want to do will not work.