It looks like according to the legal cases you cited that the states were still part of the Union, thus, the actions committed by them against the United States were treason.
I'm certain you have not read Milligan so I seriously doubt you have read Texas v. White.
The legal cases say secession is unlawful.
A review of Texas v. White indicates the whole case was a sham, much as was Scott v. Sandford.
States cannot commit treason. However, I have no doubt that the loons back then could have found two military deserters to perjure themselves to say they each saw a state commit the same overt act.