I'm lucky that my IL's thinking and ways of bringing up kids is the same (almost) as me, at least for basic manners..
Before lunch/dinner, they will not allow junk food else, how can she finish up her proper meal? They will not allow her to eat in the living room either. From young, she was taught that kitchen is the place to have dinner and now my baby is starting her solid, too sit in her bumbo seat and eat in the kitchen.
If teacher gave her sweet (as a reward for answer question correctly), my IL will ask her to wait her me to reach home and ask my permission. Even that I subscribe Vitagen and Milk for her in school, she won't dare to drink w/out mine or ILs permission.. We always explain to her not that we doesn't allow her to drink but is becoz she tends to cough easily if she take too much cold stuffs so we will take note that if she's 'cough-less' for quite some times, then she's allow to have sweets, vitagen or cold milk to a certain limit. For these, I've to thank my ILs too as they'r stern and firm on her. Least, they won't 'secretly' give forbidden food behind my back..
My ILs are those 'mine-my-own-business' type of person, hence, they won't go and bother other people's family nor to give any comment.. So, even if I brought my girls and maid back to my mum's place to stay, they won't try to 'find out' things from my maid.
Thus, i'm sure my girls are in good hands of theirs in term of upbringing.