Shadow Wolf by Suzanne Roslyn

A mistake has been made…
And wolf shifter, Jacob Grayson intends to make good on it. Years ago, he gave up his rights to claim his true mate to his brother. Now a widow with twin girls, Kasa agrees to return to her pack and raise her children, but when a stranger tries to take one of her girls, she must turn to the man who broke her heart long ago.
Jacob can’t hold back his feelings for Kasa and his need to claim her as his mate any longer. He’ll have to convince her his intentions are true this time, especially before something happens to one of those precious little girls he thinks of as his own.
When Kasa and the girls go missing, Jacob will have to rely on an unlikely source to get her back and confront the one person he never thought to see again.