Does the hotel charge for borrowing umbrellas? Is it legal?

Illegal. Borrowing things is free, and there is no "borrowing fee" in common sense and legal provisions. It is illegal for a hotel to borrow an umbrella. If guests come to borrow umbrellas, they should go to the front desk to check them. Most hotels have umbrella borrowing service at the front desk, and hotel guests can use umbrellas for free in their hotel rooms.