The meaning of 'twin share' is that the rate quoted i.e. $635 for 6 nights is for 1 person if they share with another person who also pays $635. If you want a room by yourself, the price is higher - you must pay what is usually called a 'single supplement' in addition to the twin share rate for 1 person.
When the price is quoted as 'room rate' or 'per room' or something similar, then the total price paid is $635 for however many people stay in the room.