As long as you get non-preferred rooms and do not want to rent a fridge, the 2 rooms are cheaper than a Family Suite. But, there is no guarantee of getting connecting rooms, or even rooms next door to each other. Usually Disney is very good about putting people together, but sometimes it doesn't happen.
If you get a Family Suite, you can always use the kitchenette and save money on food. We had a small order sent in from Garden Grocer, and had breakfast in the room every day but 1. With 6 people, that saved us a bunch of money!