In the first chapter of Jane Austen's Mansfield Park, Lady Betram and Mrs Norris present to Sir Thomas their idea of adopting Fanny's daughter. This will provide some relief for the Price's unmanageable burden and give the girl some opportunity she would not otherwise have.
Sir Thomas is circumspect:
He thought of his own four children, of his two sons, of cousins in love, etc
Is “cousins in love” a typo for “cousins in law” or was this phrase common in the early 19th century?