Rear door wont unlock or open

You need to remove the door panel and check the linkage. It sounds like the lock rod fall off. You should remove the seat to make access easier here is a guide to walk you through the door panel removal with diagrams below to show you what to look for in the control rods and latch.

https://www.2carpros.com/articles/door-panel-removal

Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.

Nice work, we are here to help, please use 2CarPros anytime.

You said you checked most of the fuses. You should check the specific fuse for that seat, which should be two separate fuses for Heat/position.

If the fuses are good, then you could check continuity of the circuit by removing the fuses and inserting a test light into the terminals and having someone operate the controls. If the light comes on, the circuit is fine. If not, you'll have to trace the problem.

If the circuit is good, then you're looking at a failed motor/heater.

Outside door release has failed and needs to be replaced. Either that or the latch has failed.

I assume you can open from the inside?