The Thompson Taboo — a series by H. Malcom Walker
Part of the Bloodlines of Desire universe

Mark and his sister Carrie have always gotten along well, even if she likes to tease him a little too much. A surprising DNA result leads to lines being crossed. Discover the taboo journey of two siblings caught in a web of desire and consequences. / (Reviews)

In this intense sequel to A Submissive Sibling, Nashville attorney Charlotte Thompson’s orderly world shattered when her children, Mark and Carrie, fled to an Oklahoma cattle ranch. She journeys there intending to bring them back to civilization, but it’s a trap. On the grassy prairie under the vast sky, she’ll confront forbidden desires she has long suppressed, discovering that the family she came to save is the one that will finally claim her.