Ideally, you should be able to limit it to twice a week. Let everyone in your household know that the paper will only be replaced on certain days. This will force them to use the toilet paper more sparingly. You can even take this concept to a higher level by charging per sheet for any extra toilet paper used.
Secondly, how do you unlock a toilet paper holder?
Using Nail
Toilet-paper dispensers that have the keyholes at the end of rolls can be unlocked with nails and clips. You need to insert the nail of the same diameter as of key inside the keyhole. Now push the nail in different directions and keep moving it until the dispenser is unlocked.