Loseit, my father needs your help!

My dad is 55 years old and 40 lbs overweight; it is affecting his health in many ways. I have been trying to get him to work out 3 times a week with at least a half hour of cardio every day. His main problems are a poor diet and mental exhaustion when he comes home from work. His work outs are simple using his own body weight but he struggles putting in a solid workout without tiring. My question is: WHAT SORT OF AB/CHEST WORKOUTS ARE BEST FOR STARTING OUT? These two areas are his biggest obstacles.