True. Perhaps you can point to the agreement signed before or during the Constitutional Convention that said, "if the states shall ever separate then federal property belongs to the seceding state without compensation to the other states?"
To the contrary, the states were treated as equals and thus it must be inferred that all federal property was jointly owned among them and, presuming a valid act of secession happens, should be jointly divided.
There is that big assumption again, a valid act of secession. So it makes sense that the fate of the property should have been negotiated as part of the separation, assuming a valid secession of course, and not seized before any offer of negotiation.
Not necessary. In absence of a specific governing clause that invokes otherwise, division of property defaults to either an equal dispursement based upon common status or a formulaic dispursement within the law based on degree of relationship to the former owner. Since the states were always treated on equal footing with each other in the constitution, it is safe to assume that the first case would govern.
There is that big assumption again, a valid act of secession.
You're free to dispute it and no doubt do. But that is not the point here. As I have noted, so long as one accepts it as valid the claim that others may exert over anything other than the equal dispursement of ownership of the former jointly owned properties is specious.
So it makes sense that the fate of the property should have been negotiated as part of the separation
...which brings us back to Saint Abe, who refused to have anything to do with any form of negotiation whatsoever.