Need Advice/Suggestions on our Dog situation. Has anyone experienced this?

My 7 year old boxer keeps showing aggression towards his 8 month old son. They each weigh 70 lbs! Unfortunately he's attacked him twice in the past 4 days. Over nothing. He just stays stiff and then sprints towards him quickly out of nowhere. The puppy fights back too and it has gotten ugly both times. The dad has never shown this type of behavior. In both instances, I kept trying to separate them and got bit each time. No stitches or broken bones. We now have the son(puppy) at my in-laws house for a couple days. We have 3rd dog which is the mom of the puppy. No one messes with here ever. She's sick and will pass away soon. This is all coming at us really quick. I was really sad when I got the news of losing 1 of my dogs due to sickness but now I have my other 2 fighting. My wife and I are not sure what to do. The dad is becoming aggressive and we dont want anything else to happened. Is this happening due to medical reasons, does he need training, so many questions came to our head? We have no experience with shock collars or muzzles. Any advice will help.

Edit: Dad was neutered 2 months ago. We were told we had to wait till puppy was 9 months to neuter him.