I would recommend reading them in this order. The last two really resonated with me and they have a nice range of topics and approaches to their subject matter. In Empathy they discuss both the positive impact of being empathic (breaking it down to three areas: cognitive empath, emotional empathy, and empathetic concern) and how life experiences (and other factors) can risk your ability to be empathic. Happiness touches on both the mechanisms to encourage (or provide the environment for) people to be happy and the risk (negative impact) of making it a goal for employees to achieve. All four of these books circle around common themes that I have in my own management philosophy - providing agency (ability to make decisions), transparency, respect and trust, and feedback.