Badly rusted rear door latch

[JMcDole]

Spent half an afternoon trying to open my rear door. Everything went good until I got to the latch and realized it was rusted, not the cable ends. I followed ranger station instructions, and I’m pulling up the that latch (circled in red) and the door isn’t budging at all. I pried it a bunch of times, it’s almost like whatever it connects to is broken or rusted out and not unlocking door. I have a video of that latch moving up and down but only letting me post photos here.
I don’t really know how this latch works, need someone with some expertise on this to help me get it open. Is there anything else I can pry at to unlock?
My rockers are rusted out and I think I can see the studs that hold the door latch in place, so maybe if needed I can grind them out and open that way, but that’s last resort. Please any help here. This is my first post, gonna do a Welcome thread soon. My beds off right now so I have plenty of other work to do right now, but these doors are worrying me

 

[JMcDole]

Update. I can see lower latch from inside, but still can’t get unstuck. I can’t even see how it’s latched but I can see the actual door latch.