Potty training 🚽

I have a little toddler here he's 2.5 (he'll be 3 in 4 months) he still pees and poop in a diaper but he will use the potty when you ask. What is the best way to break that so he can wear undies at night instead of pull-ups? My cousins 2yo twins are fully trained and I tried what she did and it's not working. Are boys harder to train? Help please?