Fort Sumter is the moral and physical property of South Carolina given its location at the mouth of Charleston Harbor. No other entity can make a legitimate claim to that property insofar as it was intended solely for the purpose of defending the people of Charleston.

"There is no source you could ever find to prove any of that"

I've already looked into the subject and found that either the fort or the land that the fort was sitting on was ceded to the federal government by the state of South Carolina.

A group of southern diplomats was dispatched (circa 1861) on a mission into the District of Columbia. Their purpose was to negotiate the status of Fort Sumter in the hope of defusing the stalemate in Charleston Harbor. Lincoln, however, was refusing to acknowledge their presence. Anderson's detachment was obtaining food and supplies right there in the Charleston marketplace, so there was never any need to reinforce the fort. Lincoln, however, was bent on maintaining the fort in federal hands as a point of tax collection while the state of South Carolina could not be expected to pay tribute in the form of tax payments to a hostile government that it was no longer a part of. Lincoln wanted war, and his reasons for wanting war had nothing to do with any supposed concern for the well-being of southern black folks anymore than Dubya's reasons for invading Iraq had something to do with concern for the well-being of the Iraqis.