Please check with a veterinarian, or two, or three, before you make and sell soap for animals. Products intended for humans should not be used on animals. Their skin and care requirements are quite different than for humans, and some ingredients can actually do quite a bit of harm, even to the point of death. Essential oils that are safe to use in human soap can be toxic to animals, and even kill them. Much as I love handcrafted personal care products for myself, I personally think that pet care products should be left to the professionals. The science of human skin care (solid science rather than pseudo-science published by multi-level marketing companies) is readily available for anyone willing to do a modicum of research, but that kind of information isn't nearly as common when it comes to animals.
Our own Irena (soapbuddy) here on the forums is a licensed aromatherapist. I hope she'll check in with her opinion and provide some more scientific examples of what can happen to animals exposed to essential oils and other ingredients found in human personal care products. You're welcome Irena!