Toilet training puppy’s

Hi , I know this is an old question, but need help please ! We are not new to puppies but we now have two new cavoodles we got at six weeks I think it was (allowable time to be taken from mumma from a breeder). We are having a hard time toilet training these two. We show then the dog door, take them out first thing in the morning, talk and touch grass and tell them what is is, wait for ages , one might do a wee, is praised and given a tiny treat, nothing for the other one , we finally go inside and after a minute they will both poo. This goes on and off all day, one is getting better, will poo outside and come in for a wee, but the other has no clue. They are brother and sister. What else can we do, if husband has to clean up once more think he will be out lol. We are both home with them all day everyday so they get plenty of times to be shown, we take them out to play as well not just toilet. HELP please .