Probably 80s or early 90s, saw before 1999…I could be mashing up a few movies, but I think it was all one. The grandparents were magicians and had an act where the grandpa would saw the grandma in half. Some kids scared an old man by hanging a sheet or something from his tree at night. Some kids were given cough syrup that made them cough because “people won’t buy cough syrup if they quit coughing”…and I think peanut butter made two people have really long hair…
The peanut butter hair growth remedy is from The Peanut Butter Solution>. I do think you may be mixing up some other movies though, as I don’t remember the rest of those elements.