This will vary a bit depending on whether parents are issuing the invitation or whether the couple are doing so but in general this style is acceptable:
Sally's parents are divorced but neither has re_married and are both hosting the wedding: Use the format above or if they prefer it, list Sally's mother's name on the first line and her father's on the second. Sally's parents have both remarried and are jointly hosting the wedding. Sally may wish to break with tradition and mention her step parents in which case Sally's mother and her husband's names should be on the first line with her father and his new wife's name on the second. Neither of Sally's parents is living: The invitation should be issued by whichever family member is hosting the wedding or by the couple themselves.