Wedding invitations

You don't necessarily need to have your parents on the invitation. Is this something you want? You could also say "together with their families..."

Not true. The etiquette answer is however OP and her fiancé want. Even if parents don't or can't contribute financially, many couples list parents as an honor, sometimes as co-host. When parents of the bride hosted, the parents of the groom sometimes went on the invitation by name as "son as." Hosting can also mean planning, helping to entertain guests, and contributing in countless non-financial ways. It's doesn't have to be strictly about money.

Language can be "Together with their families" or if they want to list names "Ms. Jane Doe and Mr. John Smith, together with their parents Mr. Jack Doe and Mrs. Joan Doe and Mr. Thomas Smith and Mrs. Janet Smith" request the honor/honour of your presence/ pleasure of your company etc. etc. Or the way Andrea has it is perfect as well.