Toilet training

So my son I have took out of nappies we did so at 18 months but though it was too early we tried again at 2 but after a month of wee in his pants and poo we still though he’s not ready, he’s now due to be 3 in May and will then start school nursery in September so we are now on it as I feel he should already be toilet trained my older son was by 2 and my 14 month old daughter has already volunteered to go potty even though she didn’t quiet make it bless. But for my almost 3 year old I don’t know what to do! We tried coming across calm telling him calm no wee wee and poo poo goes in the toilet we ask were does poo poo and wee wee go? He says in the toilet but he doesn’t bother. We have tried rewarding for when he’s tried but still not getting their. We have even tried a smack to the bum (which is always a last resort as I’m not a hitting type of person) and still nothing. We let him decorate and explore the toilet seat so he knows it’s his we told the older son not to touch it unless he needs the toilet to take it off and put it back on for him which we all do. I feel he’s just so lazy and it’s driving me mad I don’t know what els to do!