If 25% of parents took their children out of school then I am sure the Head Teacher would not allow any holidays. Obviously, each individual pupil would be considered ie. if a child was absent throughout the year, often, then most HT's would not approve additional time off, but if a child's attendance was good and there was an acceptable reason for the holiday, Heads are more likely to give permission unless the holiday fell between exams weeks (SAT's).
Teachers should not be allowed holidays in term-time. They are contracted to work within certain periods, and have enough holidays without the need for additional days. I doubt a Head Teacher would be happy if teachers were taking holidays when they should be teaching children, and would deal with appropriately.