Certainly complete harmony would be ideal and nice. However, kitties are a lot more like people than we give them credit. when two people decide to move in together it is natural to expect there will be some "disagreements" as the both of you settle into sharing space. Who will keep up with the dishes, do the laundry and so forth. where will your alone time spots be?
it can and probably will be the same way for your cats. however, you may be able to make the transition a bit easier for them. what bothers cats most is when a new smell invades their space. i would bring something like a kitty bed or pillow etc from one cats house to the other house. let each cat get use to smelling the scent of the other cat. you can also clean everything at kitty height. cats rub their scent on just about everything. table legs, chairs, sofa's, bed corners etc. by limiting the scent of the resident cat you can make a more neutral space for the cat being introduced. if you're going to be moving into a new place i would bring scents from each cat before moving them in together.
arguments will more than likely ensue as they get to know which is alpha. with hope and luck they will agree with each other or they will agree to disagree. try to make certain each cat has a place that is just theirs. speak softly and reassure them as often as possible. use cat nip which can actually be calming. you can also buy a plug in that will diffuse a pheromone that can calm most cats.
best of luck and keep searching for answers.