II) Have the bridesmaids wear the long version and the house party wear the short version of the same color and style dress.
3) Or give them a color and let them choose what they would like to wear!!!
III) The most common request is to have the house party wear that LBD (Little Black Dress) regardless of what the bridesmaids are wearing!!!
If you are going to have a house party, make sure it is for the right reasons! Wrong reasons would be to keep the numbers even on the altar and not because you are in competition for the largest bridal party. Take time and choose the relationships that mean a lot to you.