If you want have individuals and households to show up in alphabetical order by last name you need to enter the hh like Smith, Jane and Joe. Fine except now the greetings will be Dear Smith, Jane and Joe and the addressee will be Smith, Jane and Joe. So then one has to enter custom greetings and addressee.
My users are bad at that. Every time we send out an email or postal thing, I find I have to wade through the data and fix a bunch of them.
If you enter the HH as Jane and Joe Smith, the greetings are better; though, we'd prefer Dear Jane and Joe to Dear Jane and Joe Smith. At least if you miss one you don't end up addressing something odd. But then the sort is not by last name.
Maybe some fancy parsing with smarty in the greeting.