My invitations only come with an outer envelope and I need help with a specific situation -- My fiance has a friend that is single, but has children that we would like to invite to the wedding as well...Would I address the envelope as Mr. John Smith & guest& familyI know I am breaking a few ettiquette rules here, but this is my fiances friend and my fiance is not exactly sure of the children's names or spellings of their names so I just wanted to put '& family' for an easy way out...I know it's wrong, but I really don't think the guy we are sending it to knows ettiquette rules either, so I basically want to find the best way to word it to make it sound okay

We also don't know who his guest will be because he goes through girlfriends like underwear...But does it sound dumb to put & guest and on the next line put & family??? How would you address it?Thanks!