I don't know how, but A. K. Rose (Atlas Rose) blows my mind every time. The Institute series and Blood Ties have some crossover. I would definitely say read Ryth's story first as that is where we first met Lazarus. 
We met Kat in book one of the Institute series and I loved her immediately. Getting to know more of her back story in this book had my heart aching for her. Kat and Laz deserve the world.
Laz is such a fierce protector of those he loves. He may be a Mafia prince, but he definitely has a softer side. 
This series is so well intertwined since each book takes place at the same time. I am looking forward to the next few!!