Everything looks great with the exception of him HANGING BACK..and “ falling back” on his right side.. 1.put a ball or doorstop on outside of right foot and it will help to force him onto his left leg or you can find a down slope and let him take swings and it will force him onto his left side ..Falling back does cause slicing,for..These are 2 good fixes and there are many more ..also ,by looking at swing it’s hard to see his ball position with the driver but if it’s too far back you will fall back,also ..He actually looks like he is doing everything else a- ok…You may get him to create more leg action in his swing and the downhill drill will make him do it correctly and from there just carry it over to the golf course.He could also keep most of his weight on his left side going back and it would be very,very hard to hang back..it might feel a little weird but to stop his slice he might would try it…I like the downhill drill myself but what ever works for him..if he doesn’t like the ball under his right foot just stick a folded towel instead …( for practice only) Good luck with your FIL…