You can test everything on the door locks and latch with the door open. Makes things a lot easier when you can watch it function, or not function. All you have to do is slide the lever that locks around the door post toward the outside of the door. The biggest issues with old door locks and latches is old dried latch lube. Mopar used the old white lithium grease on the older door latches. Over time the lube dries out and becomes contaminated with dust & dirt. Cleaning them out and re-greasing them often solves many problems with the latches. You may have to pull the latch out of the door to clean and lube it.

Both outside handle and the inside handle should be able to release the latch. Sometimes you need to use a screwdriver where the post would be and pull the lever open. If the lever moves hard with both handles, the latch might simply need to be lubed.

If the outside door handle doesn't fully release the latch, the rod that goes from the latch to the handle has an adjustment. There is a joint on that rod with an Alan head set screw holding the rod in place that would often get out of adjustment. There is a small slotted hole you put the Alan wrench into to loosen the screw to adjust the rod. Usually the rod slides outward making it too long and the handle doesn't lift the3 rod enough to fully release the latch. if that is the case, you loosen the Alan set screw slightly, push the door handle fully down, and tighten the set screw. Then test again. If the inside handle doesn't open the door, the rods between the handle and the latch is probably bent more straight. I will need to be re-bent, the inside panel needs to come off to do that.

With the door open, the latch closed, and the door locked with the inside rod, the inside door handle should be able to open the latch (on the drivers door, might not work on the passenger door, I'm not sure what year the passenger door latch changed). Does the inside handle unlatch the locked door latch?
If you adjusted the outside handle, the outside door key lock may work as well. The key locks are a bit more tricky. The key has to lift the rod up past the movement inside the lever. Any wear on either end of the rod, or any wear on the handle rod hole or the latch rod holes can be the problem. There are also plastic pieces that hold the rods to the lever pieces with the holes, those too can be the problem. Then there is always the possibility the rod that has several bends in it could have been pulled straight at any of the 3 or4 bends. Either of the levers could also be damaged, or the latch itself could be defective.