thats cool. remember to get them all about the same size. they can fight if one is really small and then you have one that is really large. A nice deep substrate is good. too. the sand they try to sell at most stores are no good. eco earth would be better. we have play sand and eco earth and ours prefer the eco earth. and the deeper the better they should be able to completely dig down and be covered still to molt. usually 6 inches is needed depending on size. i know it sounds like a lot. i think we have 8 inches in the 55 gallon but its such a big tank that it works fine. although my fiance had a battle with some person on his youtube cause they said his substrate was too deep even though all serious crab websites tell you you need at least 6 inches. that was a headache.