Here is another idea for those with more than the 1 set of parents.

Use something like this.
Please join our children Mary Smith and John Doe on the date as they start their new life together blah...blah...blah
Then have all parents at the bottom in This order:
Mother of Bride and husband
Father of Bride and wife
Mther of Groom and husband
Father of Groom and wife

This way everyone is included.