Will my national park pass work here

No it will not. While the Fort itself is free to the public, the boat is operated by a third party operator.

Fort Sumter's admission is free. The boat ride to get there is a private service and so the pass is no good for that. It was $21

Yes

I'd the $21. fee for each person or family ?

Raja pagal

Yes it will

Yes, it is operated by the National Park Service