Engine will not crank

Van listed above is the Touring model.
Problem 1. Drove 120 miles, get home for a few hours, car starts again fine, back out about ten feet van shuts off. Turn the key again and only one click sound and nothing else. When key is in “on” position lights, radio, A/C, all electric seems to work. Turn key to start again and one click.
“Change oil” is written on dash. Checked oil it’s within safe zone, but a little low. I added a half a quart just in case.

Problem 2. I get a new battery and try and replace battery but hook up the terminals backward. Turn the key and horn sound and light go on. One wire starts smoking. Turn it off and unhook battery. Wire seems to have lost rubber casing, but wires seem intact. Hooked the battery up the correct way. Car starts to slowly turn over and then a loud squeal. Get it towed to a mechanic. Mechanic says ECU has a problem take it to dealership. The dealership is seventy miles away and tow would be very expensive.
Have a different mechanic take a look. He checked all the fuses with a voltmeter, and none are blown. He replaces the starter. Try with a different working battery, car slowly turns over won’t start, no squeal. When key is in “on” position electronics still work.

Problem 3. To see if the engine runs fine, we try and remove spark plugs. One snaps off the top. Now I have half a spark plug stuck in my engine.