Why won't my spark plugs tighen or loosen?

Car: Ford F150 xlt 1991 100xxx Engine: "crate" v8 about 50xxx miles, (looks like original engine)
The car was just bought so I wanted to look at the spark plugs to see if they can tell me anything about how the engine was running. I removed the spark plug cable, then with my standard spark plug socket I applied it to the spark plug and went to loosen it. To my surprise it was already loose, after 30 full turn of the socket there was no difference made… The spark plugs was still on the head.
Its like I was tightening a bolt into rubber… No difference could be made.
So after giving up I went to tighten the spark plugs and it would not tighten. So I put the plug wire back on, now after 25mph the engine shakes a little.
What's wrong with the spark plug?

Ford F-150 Truck started, ran rough. Now won't start at all. Any ideas?

1977 Ford F-150 with carburetor, 8 cylinders.

After several attempts, it started immediately (without the usual starter crank-up sound), ran loud & rough like a lawnmower. I turned it off, now it won't start.

Starter is strong, battery full, airfilter good, fresh fuel is reaching the carb. Weather is hot and slightly humid.

Anyone have a guess?

What should we do about our family vehicle situation?

My husband and I have been married for 13 very happy years and we have 6 children (ages 11, 10, 8, 7, 5 & 5).

This is the situation. We're a dual military couple, and we're retiring in a few months. We will be starting college in January, and we can't afford to keep all of our vehicles. The college that we will be going to is approximately 45 miles ONE way. We need a small commuter car for our use to and from school.

We currently own the following vehicles:
2004 Volkswagen Jetta (Paid off)
2005 Ford Focus (Paid off/Inherited from a deceased relative)
2009 Ford F-150 (Paid off/Inherited from a deceased relative)
2009 Nissan Versa (Paid off)
2010 GMC Passenger Van (Paid off)

I told my husband we should trade in the Jetta, Focus, F-150, and the Nissan in, and get a brand new car just for us to commute to school in. And we should keep the GMC as our family vehicle. But he doesn't want to do that. He wants to hold on to all of the cars for sentimental reasons, but financially speaking we won't be able to do this once we officially retire from active duty.

What should we do about our vehicle situation?

Added (1). @AlCapone: We're going to going to college on the Montomgery GI Bill. We will be getting a monthly stipend, as well as our military retirement/pension. The Jetta runs ok. It's old, and it needs some work. I would rather invest in a new vehicle.

@Cliff, unfortunately a hybrid is way out of our price range atm. But I'm looking at some of the newer models put out by some of the car manufacturers.

2001 Mercury Sable LS Cruise Control

My cruise control do sent work and I don't know where to start testing. Did a cruise control repair on a ford f150 by running a cruise test but I don't know how to run the test on a mercury. When I press the cruise on button NOTHING happens. I also noticed if I turn the key to on without starting the car to test the warning lights the cruise light doesn't turn on. It can't be the brake switch either since brake lights all work. I'm not sure if I should start by testing the cruise buttons on the steering wheel first with a multimeter or what.

I can't seem to find a fuse related to the cruise control system either unless mercury has another term for it.

Any help would be GREATLY appreciated.