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How to use "even less"?

He doesn't own a big house, even less a sports car.
or
He doesn't own a big house, and even less a sports car.
or
They weren't born in the same year, even less born in the same month, but they look like twins.
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How to use "even less"?
He doesn't own a big house, even less a sports car.
or
They weren't born in the same year, even less born in the same month, but they look like twins.
I feel "not to mention" will be better fit to your sentences.
He doesn't own a pickup truck, not to mention a sports car.
They weren't the same in the year they were born, not to mention in the month, but they look like twins.

"Even less" is an adverb to modify an adjective. It means "to a degree smaller or lesser than something/somebody mentioned before".
(EX) We cannot believe Bush's statements about Iraq. Cheney's statements are even less reliable.

paco
Comments  
In those contexts "even less" is a comparative phrase. I find that including "and" in any of the above suggests a new clause in the sentence, therefore not a clause that is comparable to the initial one. With that in mind, I'd say that the first and final sentences are more acceptable, as the second one appears more accurate with "and" omitted.
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 paco2004's reply was promoted to an answer.
could one say:
We cannot believe Bush's statements about Iraq, and even less Cheney's.

would even less ever be used by and?

for example,
This is not completely because he is lazy but because he does not have any ability, and even less does he understand how to play the game.
I think you are mixed up with the expression “much less” with "even less" which means “not to mention".

She can’t even iron her own clothes, much less cooking her own food.

He can’t even speak properly in his own tongue, much less Englsih.
Students: We have free audio pronunciation exercises.
I agree. You can use "even less" in that way.

(EX) I am not good at speaking English, and even less (=much worse) at writing.

paco