16's loyalties were still to the other androids, he just didnt share their appetite for destruction and killing, he enjoyed peace and tranquility, but it still doesnt change the fact he is an android, he is programed to kill goku, and he is the most powerful android, if you're going to add an android team at least add 16, remember only in the movie did 18 and 17 fight together, both in the anime and the manga, they only fought against one opponent at a time. 16 can still be grouped with the androids nomatter how you put it.
Or, you could have it so that you start with 18, gain your buddy, then later on you could transform and just be 16. Who cares if its not "proper" or its not 100% true to the show, i want some more diverse gameplay, im sure others do too.