If you get a litter-trained cat from shelter homes, it is fine. Normally, kittens receive training from their trained mothers. They copy and follow their mother. Use similar litter-trays as your kittens were accustomed to at their shelters. While litter training your kittens, allot a separate litter box and an extra one for each kitten, and cat in the house. Place this preferably in a private but easily accessible place, away from noises and disturbances. Also, place it away from feeding areas and dark basements. A litter tray should be sufficiently large and deep to prevent any spillage of litter when they dig. Although open trays are a good idea, some prefer hooded trays to get more privacy. Remove and change soiled litter daily. Empty the tray completely once every week and clean it with detergent and hot water. Do not use disinfectants, as cats are allergic to disinfectants. 

Litter Kitten Training

 While litter kitten training cat, stick to a single training option irrespective of the time it takes for your cat to accept this training technique. If you change the technique, it will only cause confusion.