Are there dentures you can have for a harelip?

Sure. See a maxillofacial prosthodontist for the best results. Specially trained just for this type of treatment. You will find one in ca, probably not far away. It is worth the trip. Good luck.
Yes. You can see a prosthodontist who is a specialist in reconstructive prosthesis for cleft palate.
Yes. See your local prosthodontist, a specialist in dentures.
Depends. If you are referring to a cleft palate, upper dentures can be fabricated with an obturator to close the opening to the sinus area and seal the palate. Cleft lip would need cosmetic surgery.
Do not know. This is best answered by a specialist in plastic and reconstructive surgery.