yeah 1:3 or even 1:4 would be fine. Those are some calmer mbuna species and should be okay with the OB. I've had Rainbow Shark with no problems in my tank and the make a great addition! I'd still probably get rid of the Blue Dolphin....I believe those can get up to 8 inches big, which is just too much for a 55gal tank. If you do decide to get rid of it, you could add another species of mbuna with the 1:3 or 1:4 ratio....hope this helps