Spent some time at the cabin this past weekend and found three major issues. Made a temporary fix to Problem 2, but need to go back and make a better fix once I have some solid jacks and materials to support the cabin while I make an official repair.
Here's what I'm seeing in the photos. Problem 1 - Looks like someone cut straight through both 2x8's and then tried to patch it with one 2x6 patch on the inside. Clearly, you can see how this didn't work. I didn't look at this one any more, because I found Problem 2, which was much worse.
Problem 2 - shown in photos 2a and 2b - shows where only one of the 2x8's is actually sitting on the support post. Over time, the stress of the cabin weight has twisted this 2x8 and it's starting to crack at the bottom from the stress. The outside 2x8 appears to be badly damaged. As a fix for now, I've notched a pressure treated 2x8 in the middle so it would fix over the 6" support top and pounded it in place to support the floor joists above. It was very tight. Then I bolted it to the existing frame to help hold it in place because I could not get it up against the existing 2x8 (it was too tight a fit). Again, not a real fix, but thinking it will help support what's there without doing any more damage. (The metal post is quite solid, which was the only good news for the day.) By the time I was done, I wasn't in the picture taking mood, but will do so when I'm out there again, likely this weekend.
Last but not least, Problem 3. Looks like something has been eating on the inside of one of the corner joists. The wood is solid around the damage, so assuming I can get away with sistering in a pressure treated 2x8 to fix it. Fortunately, except for Problem 2, all other supports appear to be supporting both 2x8's.
Eventually I will need to find a better way to support the cabin. Thinking building up a block foundation on either side of the existing metal posts, but need plenty of advice prior to doing it to verify I don't damage what's there.