Not without amending state Consitutions they couldn't because every southern state that participated in the rebellion had clauses preventing the legislature from passing any laws abolishing slavery. And if any southern state got a wild hair up and decided to end slavery, the confederate constitution guaranteed that anyone "shall have the right of transit and sojourn in any State of this Confederacy, with their slaves and other property..." So individual states couldn't ban slavery within their borders.
The Confederacy did enact a law that required that Union slaves captured on Union ships to be returned to the state of origin and freed by that state's Governor.
Union slaves on Union ships? Assuming such an incident occured, how could the confederate congress require a Union governor to free a slave?
Nonsense. Sojourn/travel with slaves/servants, but not move into a Confederate state that banned slavery and keep their slaves.
Union slaves on Union ships? Assuming such an incident occured, how could the confederate congress require a Union governor to free a slave?
You mean a Union governor wouldn't? If Lincoln could (allegedly) free slaves in the Confederate states, why could they return the favor?