No I think you have the perfect size tank to grow them out and get a pair in. give them time to settle in and theyll be all over again
how long have you had the tank running and whats your water perameters? the current is good. also it seems to me that they are al trying to hide and seek refuge in the same spot. if they dont start becoming more social and active in a week or so maybe try to add a couple more spots to get away or remove the hiding spots in the slate. what are you feeding them?