I had the same thing too - but eventually they'll learn that it's ok to do it at Grandma's house, not ok to do it at home.
I love my parents and my mom-in-law and I don't want to cause any friction/tension - I tell them once in a nice way, I don't like it, don't want to do it, etc. Then if I see the behavior - then I tell her that you can do it at grandma's house, but not here!
Consistency is the key - 14 mos is young, but just be consistent as you can.
I have two girls - 15 mos and 3 1/2 yo and they know...they just do. Pick your battles!! My mom lets the kids watch TV all day, but they can't at my house! My mom-in-law lets them eat butter (but not at my house!). :)
Use your best judgment...