Thought they could? Or didn't care what their constitution said? After all they ignored the requirement to establish the third branch of government. What was ignoring the slavery protections compared to that? Who was going to tell them they couldn't?
We've already discussed this. See above.
Authorized how? Was their legislation approving an end to slavery in exchange for recognition? If so, when was it passed?
By giving their consent to appoint an ambassador with plenipotentiary powers.
Really? Name one member of the Confederate Supreme Court.
Why would that be relevant?
Nonsense. You have offered your completely bogus, unsupported claim that their actions were constitutional, despite the fact that the constitution clearly prohibited them, by offering some lame explanation that "treaties madde them constitutional." That is completely false. Treaties cannot override the constitution, not even the Confederate one.
By giving their consent to appoint an ambassador with plenipotentiary powers.
Did they give their approval? If so, when?
Why would that be relevant?
It would be proof that the court existed and that Davis and his congress had not ignored their constitution in that area, and would provide evidence that Davis might not be willing to ignore his constitution in other areas.