Let's see...max size 3'6", that's around 42" TL....and with them being what I think are walking benthic sharks....that comes to around 3.5x for length and 1.5x width, so 147"x63".
Formula and explanation here. And even if they're an inactive benthic, that's still 3x by 1.5x. So 126"x63"
Do you have space/money for a 12' by 5' pond? And that's not even accounting for the depth of the tank as well....or the feeding costs...
As for the "minimum tank size"....I really feel that LiveAquaria just doesn't do the larger saltwater fish justice, and recommends 180 gallons as a blanket size for them regardless of how large they actually get....