Matching and highlighting addresses in a address book

I'm using Excel 2010 and I have a copy of an address in Excel.
I'm trying to identify all the people who live by themselves- without partners and spouses.
I have a column array like this:
A B C D E F G H I J K L M N O P Q R S T
PD ENO Status Title First Names Initials Surname Suffix Date of Attainment Franchise Flag Address 1 Address 2 Address 3 Address 4 Address 5 Address 6 Address 7 Address 8 Address 9 Postcode

And the relevant columns is usually L. I am trying to figure out the formula that allow me to extract or at least highlight the people who live by themselves- or alternatively the people who live in the same house (which would therefore identify by exclusion the singletons)

Thanks