who owns copyright of a drawing done by multiple artists?

I asked a friend of mine, artist A, to design a tattoo for me. There are three parts of the tattoo: Vetruvian man (public domain), a DNA molecule, and a version of the "darwin fish." (with its own copyright history) I gave me something, but I wasn't thrilled and I asked another friend, artist B, to swap some things out and change it. He gave me something, but it wasn't finished because lines weren't connected and scaling was off. The tattoo artist, artist C, finished the design and put it on my leg. Now, however, I would like to make this tripartite symbol my personal trademark and logo on my website and the jacket of my book. I won't sell it as merchandise, but hopefully it will help me brand myself and establish identity and recognition. I went back to artist A to take the final symbol from my tattoo and render it as a digital drawing in both detailed and silhouette versions. My question - who owns this piece? Three different artists contributed pieces of it, but separate from one another and always at my direction. Two of the three were paid by me to do so. It sounds like I am free to copyright this, no? Or do I need to get copyright transfer agreements from all of them (and offer to pay them)? Well, not the tattoo artist - copyright transfer is implied when tattoo art is purchased. (right?!)