I don't know of any way to open it without using those levers and some force. The latch mechanism bolts into the bottom of the gate and the part it grabs on the bottom of the truck is also bolted in place. From what it looks like, someone got the hatch on mine open with a crowbar before I bought it. They had the door held closed with a ratchet strap. If you can get the whole plastic panel off from the inside that will help you work on it. Something like PB blaster and lots of patience will hopefully get it done. Gotta get the penetrant into the bottom of that latch from the top and work the door in and out while moving those latch arms up (I think, been awhile).
The key stuck issue is separate, I freed mine with penetrant and working the key back and forth. Spray it into the key hole.
Here's a video that explains a bit how the latch works and you can see where you need to get the lube.
YouTube
This one is pretty much what you need to do to get it open.
YouTube