Is wiping over the last two socks valid if wiping over the first two socks became invalid? And which two socks should a person performing ablution wipe over if they wore two socks over two socks while in a state of ablution?

It is not permissible to wipe over socks worn over other socks while in a state of ritual impurity (حدث), because wiping requires that they be worn while in a state of purity (طهارة). Therefore, whoever wears two pairs of socks over two other pairs while in a state of ritual impurity, their wiping is invalid and their prayer is incorrect, and they must repeat it. However, if one wears two pairs of socks while in a state of purity, and then wears two other pairs over them before becoming impure, it is permissible to wipe over the upper two pairs according to some scholars, because they were worn while in a state of purity.