There are only few "multiple resorts" in one, most of the other resorts are just twins that somehow are categorized as two different resorts but are same.
Example multiple resorts:
Barcelo Bavaro (Palace & Beach)
Fiesta Palladium (Bavaro, Punta Cana, Palace)
RIU (Pallace bavaro 5*+, Palace Punta Cana 5*, Palace macao 4*+, Bambu 4*, Naiboa 4*)
Iberostar (Dominicana 4*+, Punta Cana 4*+, Grand Bavaro 5*+)
Majestic (Elegance 5*, Colonial 4*+)
Princess (Caribe Club 4*, Tropical 3*+)
Twin resorts (basically the same thing, one or two receptions but the same facilities). usually one resort form one side of the road to the beach, and the other resort from the other side.
Melia (Caribe, Tropical)
Ocean (Blue, Sand)
BeLive (Bavaro, Punta Cana, now merged)
Bahia Principe (Bavaro, Punta Cana)
Hard Rock (don't know the names, so let's just call it the first and second)