Start by trying to book a reservation for 8. There are not that many large tables, but with a single res for your whole group you have a better chance of being seated together or near each other.
If you cannot find a res for 8, you can try for 2 smaller reservations at the same time and ask to be seated together when you check in. The castmembers will do their best, but it is only a request. You may have to wait longer or you may end up seated at 2 separate tables because there are no large tables available. To make 2 separate reservations for the same timeframe you will need to make the second res in someone else's name and account.