Does each person on my account or project need their own paid account?

Understand how members are counted

No. Everyone who you invite to become a member of your project will need a login with SyncSketch - but will not need a paid subscription themselves. Learn more about Member Limits.

Note that you can make a Project public and share review links to anyone, and those guests do not need a SyncSketch account at all. (Obviously this is not practical for a commercial undertaking, and there is more limited functionality with respect to users who are not members of your project.)