Four in Hand by Stephanie Laurens

The Duke of Twyford is forced to give up his hedonistic lifestyle when he is sworn to protect the four Twinning sisters. But he soon finds himself fighting to guard the oldest sister, Caroline, from the biggest rogue of all -- himself!

Impetuous Innocent by Stephanie Laurens

After her father's death, Georgiana Hartley found herself at the mercy of her lecherous cousin. Seeking refuge at the neighboring estate, she came across a danger of another sort in the form of Dominic Ridgely, Viscount Alton of Candlewick, who was only too willing to help her, even in such a highly improper situation.