Again, if you would read the instructions then there is no doubt as to their purpose. Their mandate was 'the purpose of negotiating friendly relations between that government and the Confederate States of America'. Nothing there indicates that any possible outcome other than recognition of the legitimacy of the southern rebellion was possible. Your claim at negotiation involved no negotiations at all.
Meaningless lip service.
Along the same lines as your claim that the southerners would fairly compensate for property already seized, a claim not included in the mandate approved by the confederate congress BTW.
All three of the other forts that SC had "seized" were bought and paid for by SC long before the federal government even had a regular army.
Absolute nonsense and, since the Davis regime also held mints and armories and forts and facilities throughout the south with no evidence that they ever meant to pay for them, irrelevant besides.
You are neglecting the first rule of diplomacy. In negotiations practically everything is on the table no matter how adamant one side or the other is about a given position. That doesn't mean a side will cave, but it does mean that there is always room to work. Applying your horrendous illogic, one could similarly say that by Lincoln's declarations that secession would not be permitted, the confederates had no reason to seek out a meeting with him for negotiation. Yet they did because they, being wiser than Lincoln, saw it a worthiable aim to at least attempt peace.
Along the same lines as your claim that the southerners would fairly compensate for property already seized Not at all. They had the papers and expressed every intention of paying.
a claim not included in the mandate approved by the confederate congress BTW.
Your timeline is out of order. The confederate congress did not even exist yet when the first team of negotiators arrived in Washington with sanction from their states to negotiate payment.