Start by trying to book a single reservation for 10 so that the restaurants are aware of your party size. Large tables aren't as plentiful as smaller sized tables so even though you are able to book a reservation for 10, when you arrive at the restaurant it will depend on whether there is a 10 top available, whether large parties seated before you leave in a timely manner, how busy the restaurant is. Just be aware that even with a single reservation for 10, you might be seated at more than one table.
If there are no reservations for 10 available, try smaller numbers (e.g. 5 & 5, 4 & 6) for reservations close to one another in time, but you will have to make the second reservation in the name and account of a second person in the group. Once you arrive at the restaurants, you can request to be seated together or near one another, but it is only a request and may not be possible. The restaurants expected two separate smaller parties so it may not be possible to be honor a request to be seated together. You might be lucky, you might have to wait longer or you might be seated at tables on opposite sides of the room.
If you call the dining reservations line they can see if any reservations are available, but typically it is the same as what is available online. They cannot combine two smaller reservations unless a larger table is available. The final seating decision is made by the restaurant staff at the time you arrive for your reservation.