im going to set up a 15 gallon tang tank with the attention of a couple fish, i want some shellis or some other fish, i like caudopunctatus, and i like brevis, or brichadi and i would like to know if i could have 1 pair of thoughs, or if it is posibal to have 2 pair of different species, or if there are any othere type i could have, thank you for your help