MB4 248a: Who Can or Should Nullify Their Reshus (380:4); Retracting a Nullification (381:1)

If there are only two people in a chatzer and one person  nullifies his chatzer (but not his house) to the other resident they can't carry from his house into the chatzer.

If two people didn't make an eruv in a three-person chatzer and they nullify their reshut to the third, they don't need an eruv.

Does it work if Levi nullifies his reshut to Shimon and Shimon nullifies his reshut to Reuven?

If Reuven nullifies his reshut and then carries from his house into the courtyard he ruins the eruv for everyone if it was intentional - he undoes his nullification.