I think, and I speak very warily on a situation with which I am not familiar with, but I think the way forward is to approach your son obliquely on this subject, coming from it, perhaps from your son's side of the problem.
Praise the good aspects of him. Is he, temper apart, a good and loving husband and son? Talk about other things in his life that show him up as a caring person, tell him how much you love and admire him then suggest that -he- must find it so frustrating that when there is so much that is good about him that he loses his temper so easily. Perhaps let this conversation arise when you are involved in a shared, enjoyable occupation where he is helping you - cooking, gardening or something like there.
You could, perhaps, talk to his wife first, again from a sideways approach. Tell her how frustrating and worrying you find his temper loss and how you are reaching a limit. Ask her how she feels about it. Let her know how much you love your son and all that is good in him, make it look as a joint approach to help someone both of you love. Let her feel at one with you in approaching your son.
It might be worth seeking professional help before you approach your son. Talk to a Counsellor or Psychologist about the problem and seek their advice on the best way to deal with this problem