My son was slow to train as well. Number 1 was very easy once I stopped using the pullups and used the old fashion cloth training pants. I used pullups at night, but he woke up dry from the very start. Number 2 was a little harder to do. He would use the potty for Number 1 and then poop in the pants. He eventually got it right, but it wasn't until he was about 4 1/2 years old. He trained himself just in time to enter PreK4 school. Your SIL may need some parenting classes. Your grandson sounds like he just needs maturity time. Good luck.