Well I cant help with them being with calls or east indies. But I can say that when I added my two muscovies to my small backyard flock, my rouens where the nicest little things to them. I have both a male and female, and they both took care of them. They are the ones that showed them where the food and water was. I have to say I LOVE my rouens personality to other ducks. I even have Mandarins in a pen right next to their and they see each other through the gate. They go and lay next to the fence and try and cuddle with the Mandy's. It cute! So I think you will be okay with them being with calls or indies.
The best way to introduce them is to seperate an area for the new ones where they can all see each other but not touch each other. I always put their food right next to the fence that is seperating them. Eating together get them bonded more. When they all lay next to the fence all day long and act like they are best friends then you can put them together.
When you do put them together completely just watch them. There will be some pecking and pushing down on each other. But they are just establishing a pecking order. You can definately tell when it is aggresion rather than pecking order. Agression is when one duck chases another relentlesly trying to get it. Since there will be such a size difference, watch them closely. The rouens will most likely be the top bird because they are bigger. In being so they will peck the call or indies, but it should only last a few days then they should settle down.
