TIFU by asking my aunt her mom's age

For context: my family tree is hella fucked up cus one of my grandpas sleeps around a lot. He's now 75 with 30+ children (most illegitimate and around 10 from his current/previous marriages). He got with his current wife around 15 years ago and they have 2 children, J (M14) and S (F13). How did he get so much tail? Idk prob cus he was in the army and was an athlete (never made it to a professional leaugue tho) and is still hella fit and mobile to this day (my guy did 2 pushups on 3 fingers and folded himself in half last week according to S😭). How the hell is he still able to have kids in his age? At this point I dont even know

So my grandpa and his current family visited my house earlier this morning. He talked with the adults at the house and made me sit with his children and watch them. We were making jokes n stuff and I asked what it's like to have a 75yo dad and jokingly asked how old their mom was. We were sitting beside the table where the adults were so S asked her mom how old she was and her mom replied that she just turned 31 earlier this march. S joked about them having a 44 year age gap but then we realized that it was kinda concerning so we did the math: 31 - 14 (J's current age) = 17 and 75 - 14 = 61.

The whole family exhanged glances and glared at him. They all blow up at my grandpa for sleeping around with a 16/17yo when he himself was 60/61 and how he's mentally sick in the head. There were a lot of hysteria and a lot of apologies toward S and J for how the adults didn't notice what was going on while their mom was defending my grandpa. Now my entire family is broken up and one of my aunts (still one of his children but shes 27yo) is considering calling the police on him.

TL;DR joked about my grandpa and his current wife's age gap with their child (technically my aunt but shes younger than me so idk if i should call her that) and jokingly asked her for her mom's age. Did the math and found out my grandpa fucked a minor in his 60s

Edit for clarification (placed it in a comment but more people would prob see it here):

We don't see him that often since he lives 700+km away from us and he only visits once a year before my grandma's (his sister) birthday. Yes, my family knew about his behaviour towards younger girls but we always assumed he went for college girls who are of legal age. We are not close to his wife and don't have any contact with her other than through my grandpa and their children. We never stopped to question his wife's age since she looks older than her age and we assumed that they got together when she was in college.

Edit #2: Ok so S just told me that he's supposed to be reffered as GRAND-UNCLE and NOT grandpa😭 my bad yall my native launguage only uses 1 word to refer to both (Lolo)