You could just take control of the situation by taking charge. Say that while you appreciate their busy schedule, this does nothing to excuse them not being fully committed and the only person it effects negatively is their child and it can not carry on. I appreciate for us daycare providers that toilet training is difficult but I don't believe it is more the parents job than mine and I don't think saying anything along those lines directly to the parents is productive regardless of what you actually do feel. Tell them, honestly tell them, don't ask, that they have to be 100% on board even if it's after the worst work day of their lives, no excuses. Make it clear that the minute they aren't, you will stop training all together because if this isn't a collaborative deal, then your efforts are wasted and it send mixed signals to the child. This way or no way and then you need to follow through enforcing that.