Creating new, custom household greeting

Any help would be greatly appreciated!

I am using Nonprofit Success Pack, and my organization already uses all three household greeting fields:

Household name: just the name for the household record

Formal greeting: (ex. Mr. Thomas Jones and Ms. Wendy Jones) first line in an address

Informal greeting: (ex. Mr. Jones and Ms. Jones) follows "Dear" in a letter

We want to create a fourth field, which would be a really informal greeting, based upon what is entered in the "informal salutation" field in contact records. For example, Thomas Jones might go by the name "Tom," and that is listed as his informal salutation in his contact record. Therefore, I want the new, customized field I'm trying to create to read "Tom and Wendy."

The problem I'm running into is how to pull the names from the contact record on an account object and, more importantly, how to make the text field conditional: IF there is a second person, THEN add the word "and" and the next name; IF there's a third person in the household, THEN add a comma first, the name, ... and then add the word "and" with the final person listed.

Is what I am trying to do possible? If not, does anyone have any suggestion of how we could navigate this? I considered changing the household name format to work as the first line in a block address, but I don't think we want to do that.