Sci-Fi has a great atmosphere, but the food is barely mediocre. Your group will have to split up there and it's not designed to make conversation easy -- at least with those in the same "car." I'd visit Sci-Fi for an afternoon snack.
50's Prime Time could more easily accommodate your group, and when you check-in just ask them to put some tables together for your group. The servers tend to vary, so if you are interested in lots of interaction, mention that when you check-in. Some areas tend to have servers that are somewhat restrained. And the servers do tend to "read" the group and react accordingly.
The food at 50's is much, much better -- a wider variety than burgers and fries fare at Sci-Fi. And after you clean your plate you can share some S'mores or a Dad's Sundae! YUM!