1.

Mr Smith uses his photo driving licence for proof of identity. Although it has his address, he can't use it for proof of address as he has already used it as proof of identity.

He could use another document as his proof of address (such as his latest bankstatement) or he could use his passport as proof of identity instead, that will allow him to use the driving licence as proof of address.

2.

Mr Smith uses his bank statement as proof of address. Although it is a joint account with his wife, Mrs Smith, she cannot use it as proof of address as it has already been used for Mr Smith's proof of address.

Either Mr Smith or Mrs Smith is going to have to use a different proof of address. For example Mr Smith could use an electric bill dated within the last 3 months and Mrs Smith could use that joint bank statement.