B

Oh dear. I would be very concerned! I think the only answer is you can’t leave him there overnight any more, certainly not for an extended period of time and certainly not when he needs to be in school in the day. My kids have a later bedtime and more snacks at grandparents house, I think that’s pretty normal, but that’s only the odd weekend and occasionally in holidays. I’d honestly be tempted to just stop sending him there unless it’s a time when it doesn’t matter that he’s going to have all the sugar and little sleep. Don’t even necessarily have to have an argument and tell her that’s what you’re doing, just… stop doing it. If she questions it be honest and say that you weren’t ok with him having that sort of diet/bedtime routinely or for longer periods of time, and as she had made it clear she wasn’t going to change you are now only sending him when those rules are ok, which won’t include days when he should be in kindergarten or anything more than a night at a time (or whatever you are happy with).

The telling him to lie to you thing is a bigger issue and she needs to be told to pack that in or he doesn’t go at all. But if the situation is that he only goes when you’re ok with her rules, there’ll also be no need for her to tell him to lie. I’d keep an eye on that though.