Never ordered from Pet Solutions. It's hit or miss with 2 coral banded shrimp. My dad got a pair and they did fine together, but we know they were a pair. Caught them ourselves. They were hanging out under the same rock. In a different tank he had one and then I gave him one of mine. We thought they had paired up too, but after a couple of days one of them disappeared. Pretty sure the other one killed it. So I guess it's hit or miss.
As for 2 mandarins, I suggest not getting them. You have a 75 gallon right? They probably would run out of pods. I have two that eat pellets and other frozen foods in my 150 gallon together. A male target and a female green. They are both fat, but they do not like one another. The target, who's the larger one, will chase the female if he sees her. I'll be fishing one of them out when I set up my next tank. Thank fully the female is quick and can get away from the male pretty easily and they generally stay on opposite sides of the tank.