“From what I’ve read when the southern states rebelled they immediately began seizing anything that they desired.”
You should read “The Confederacy”, by Charles Roland.
The confederacy did not immediately go out and seize forts. Rather, they immediately sent a peace delegation to Washington DC, and offered:
- to pay a fair share of the federal debt
- to PURCHASE all federal installations in the south
- free passage of the Mississippi river.
That’s the first thing they did, if you’d like to know.
Now, just about every one of the installations you listed has something in common: No bloodshed. The local confederates knocked on the door, and the personnel (often one man) were told their time was up. And the personnel were allowed free passage to the north. Really only two forts held out, Sumter being one of them. Seems downright gentlemanlike.
So if I knock on your door, tell you to get out otherwise I'll blow your house up, and you do then does that mean I legally own it?
Confederate President Davis well knew that only Congress could deal with such issues, and yet he never dealt with Congress.
Instead he sent emissaries to negotiate with President Buchanan, who had no such authority and so refused to deal directly with them.
But in no case was Davis serious, when you consider that our Founder Benjamin Franklin spent many years in Britain attempting to negotiate a better deal for Americans before reluctantly giving it up in 1776.
By contrast, Davis' emissaries spent a few weeks talking to the wrong people, then gave it up and went home so Davis could launch his Civil War.