I have two female (one target, one green) mandarins in my 90 gal tank. I've got a fuge to keep my pods going as well as some cheato in the display. My target mandarin (despite being the smaller of the two and added several months after the green) is the boss.

If your 125 is well established with a strong pod population, you should be fine with two. If you decide to go the male/female route, make sure the male is larger than the female by a fair amount. Otherwise, the female is very likely to kill him (it happened to my last male green mandarin).