Need to see the manufacturer spec. If you throw one new tire on a Subaru or other AWD vehicle and the other three are worn, have smaller diameter, the AWD system will think the new, larger tire is rotating slower and apply traction to the other wheels, eventually may fry your center diff. or other components.

If the puncture is in the tread and not the sidewall have the tire plugged. If the tires are all worn to 3/32 replace the tires.

No. It is certainly not true of my 4 wheel drive vehicle.

I always ensure that tyres on the same axle have similar tread depth and pattern but, otherwise, I replace only the damaged tyre.

Nope complete myth!

The military wouldn'T get very far if they had to change 8 wheels each time would they.

The real answer is, you're not providing enough information to properly answer the question.

On the face of it, NO.

nope, but it should be the same size. tires naturally wear differently on all 4 corners depending on your driving style.

No. Even if it can't be fixed, you can find a matching size and wear at a salvage yard.

If the tires are worn and the tire cannot be fixed, yes.

Not true.

no