I saw two cars in the garage, one at the far end and one near the entrance.

I saw to cars at the crime scene, one destroyed and the other fine.

I saw two cars that the crime scene, one gradually moving, the other not moving.

I saw two cars at the crime scence, one being used to hide the carnage.

I saw two cars at the crime scene, one with its radio on.

1. Can I have the name for this construction please?

2. Is it ever preferred to write it as a full relative clause? (eg. one of which was at the far end of the garage...)

1. To my knowledge it has no special name.
2. Some people may prefer a complete relative clause in some contexts. Language isn't math. There are no rules that always apply in every situation.

[:^)] Does anyone know this?
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 Cool Breeze's reply was promoted to an answer.
If the question is on the "highlighted" structures, I am willing to wager a BigMag on caliing them "noun phrases" which is functionally adverbially modifying "the two cars".