Oh my, I wonder why you'd want to date another couple. I'd imagine that dating one person would already create more issues and troubles that one person can handle, but adding more people to the equation? I'd advice against this because while there is a potential for things to be very fun and dandy, there is also potential for it to turn sour quickly with numerous complications. Think about sexually transmitted diseases and hurt feelings.
By dating a couple....do you mean that you would want to go out with 2 people at the same time with both of their knowledge and enter a relationship with the couple? I think you mean polyamory. I will have to say that that can be rather rare niche to find in the dating world, as this form of relationship is generally frowned upon by most of mainstream society. Just google it and you can probably find some answers.