My friend in singapore has a split type aircon that has just 1 external unit connected to 4 internal units in different rooms. I find that convenient. Don't know if that is available here or if it may cost more.
I myself bought a new home with window type aircon holes in each room. I had to buy window type aircons rather than the split type because it would cost me more installing all of them. I bought Panasonic since it gave a higher EER that its counterparts, although the split type gave even a much higher EER.
Yes, i think there's an available single external unit with two internal units but the trouble comes when the external unit needs to be fixed, in case.Both rooms will suffer.