The fins were actually done that way to keep them canon with my story: Shapeshifters can take on any shape with the same number of limbs - a head, tail, and four appendages. They can do cetaceans (whales, dolphins) and pinnipeds (seals, walruses, etc) but not fish or invertebrates. I suppose I could have given them dolphin butts but that wouldn't be sexy...
For the record, Daecon (white hair) is the only one of them who can do hybrid forms, and when I did the first drawing he would have been the only one who could do a half human, half sea creature. When I did the second one I wanted Evander to get in on the fun so I made an exception for him. They are going to use these forms in an upcoming Inksgiving special story