Not really, no. Sumter was built long after the Revolution on land deeded to the U.S. government free and clear by act of the South Carolina legislature.
Secession... both times.
Nonsense. What you're saying is that there was nothing that transferred ownership. The Confederacy chose war to take the fort by force and as that didn't turn out quite the way y'all hoped.
I don’t recall the crown just handing over land.
People have a moral right to govern themselves the way they see fit....but they can also be hit on the head for exercising that right.
The South risked everything in order to create a slave-based empire and lost. Better luck next time.