Have you tried 8? Odd-numbered tables are harder to come by sometimes. If you have an ADR for 8 and show up with 7, it's not a problem. If it's still a reservation you cannot get, you might consider joining the Landry's Club and getting a membership card for a small fee. Then you can call the restaurant directly to make the reservation. They seem to set aside some tables for Landry's members at Y&Y. We dined there several years ago with 12 of us, so I know they can move some tables together at times. I'm pretty sure we did that by calling and using our membership.
Another option is to get 2 people in your group to book 2 tables of 4 around the same time. Then show up a little earlier and let them know you'd like to be together. They often (but not always) can accommodate that. You just cannot make both ADRs under ..the same person around the same time.