the powder brown/blue might fight with each other b/c they are very similar to each other. and as you already know are hard to take care of, right along with hippos.
there are plenty of other options as far as tangs go. look at maybe a kole or cheveron tang. both stay small and are hardy.
a brown scopas or yellow tang wouldnt be bad either.
a naso will get way to large for a 125, just like a valmigli tang or unicorn tang.
there are loads of other nice colorful fish outside of the tang family, like angelfish, foxface, wrasse, etc.