Very sorry to hear of this little bloke's problem. I was very lucky 3 kids & 3 out of nappies by 2 years. I'd like to travel the 900 apply a bit of pressure the 2 Testosterone bearing bags SIL has.
I was lucky my 2nd much loved husband thought the toilet was the most comfortable seat in the house so would sit with youngest daughter for ages. When anything was accomplished it was like scoring a goal in a football match to us on the outside LOL