no slime coat sucking but def territorial.. and I should note I had the reticulated version so they may be a more aggressive fish. I would expect mollys to be fine with them but guppies might be a "test". I never tried a "group" of them but have heard that they do well in groups. I would just avoid trying to put a "pair" in a tank personally. But this is pretty typical of loaches in general, and I shoulda known better...