It is better to have one person make a reservation for the maximum number of people who will be dining at the restaurant. This way the restaurant will know that you all want to sit together. If you make 2 separate reservations, they cannot be connected in advance and they will be for 2 smaller tables so you will have to ask to be seated together when you check in. While CMs will do their best, there is no guarantee that there will be a large enough table available for your whole group so you could end up seated at 2 separate tables near each other or at opposite ends of the restaurant.