Lands that produce mana based only on what other lands "could produce" won't help each other unless some other land allows one of them to actually produce some type of mana. For example, if you control an Exotic Orchard and your opponent controls an Exotic Orchard and a Reflecting Pool, none of those lands would produce mana if their mana abilities were activated. On the other hand, if you control a Forest and an Exotic Orchard, and your opponent controls an Exotic Orchard and a Reflecting Pool, then each of those lands can be tapped to produce {G}. Your opponent's Exotic Orchard can produce {G} because you control a Forest. Your Exotic Orchard and your opponent's Reflecting Pool can each produce {G} because your opponent's Exotic Orchard can produce {G}.