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my family definition: A family is a group of related species, morphologically similiar, who share a set of physical characteristics, which are not posessed in total by any other group.

What sounds easy in theory often turns out to rather difficult to do in practice. As an example, this definition...

For the felines for example, they would be placental carnivore mammals that have retractable claws.

...is broken right off the bat. Your definition of "felines" excludes cheetahs but includes sea otters. Keep trying ;)

Proving, I suppose, that sea otters evolved from cats whilst cheetas did not. I have a sneaking suspecion that the technical details of the sea otters claws are disimilar in structure to that of the cats, and that the cheetah retains the similiar structure, in fact cheetah claws can partially retract.

OK, how many of THESE cat traits does an otter have...

The structure of the felid eye shows various adaptations for increased visual acuity. The pupil and the lens, in the eye of an animal capable of seeing in very dim light, are much enlarged relative to the size of the retina, the layer of light sensitive cells at the back of the eye. The high proportion of extremely light sensative cells in the retina (rods), compared to the cells optimized for vision in high intensity lighting (cones), allows the felids to be well suited for low light conditions. The retina in nocturnal animals, including the cats, are rendered even more effective by the addition of a reflective layer behind the retina, the tapetum lucidum. Light that has passed through the retina without being absorbed, and therefore not sensed by the cells of the retina, is reflected by the tapetum, passes back through the retina, and thus has another chanse of being registered by a detector cell. The light that is not detected by the retina, during both passes through the eye, is reflected out of the eye through the pupil and creates the distinctive yellow-green eyeshine when observing cats at night. The eye structure of the felids greatly improves the light gathering ability of the eyes and results in night vision about six times better than that of humans.

The tongue of the cat is peculiar among the carnivores. Although it is primairly a body cleaning tool, it is also an important part of the feeding apparatus. The upper surface of the tongue is covered with short pointed projections called papillae, giving it the apperance of a wood rasp. Although small and somewhat insignificant in the house cats, the papillae of large cats are fromidable instruments. Scraps of meat and other food items are easily separated from the surface of bone by passing the tongue over the area to be cleaned. Hand feeding captive cubs is often aided by the insertion of a finger into the mouth, initiating the succling instinct, and quickly replacing it with the nipple of the bottle. This sucking on fingers and thumbs is apparently enjoyable for the felids, as it is for the humans, and the process is often observed with adult cats and their handlers. Thumb sucking by adult felids often results in bleeding thumbs and fingers, actually scraped raw by the rasping action of the papillae on the skin.

Dentition is reduced in felids; shortening the jaw results in increased force at the bite point. The dental formula is 3/3, 1/1, 2-3/2, 1/1 = 28-30. The incisors are small and chisel-like. The canines vary from medium-sized to enormous in the extinct sabertooth cats. The upper canine is larger than the lower. The first premolar is absent; the second, when present, is atrophied. The molar is small and simple in structure. Carnassials are very well developed and cheek teeth are exclusively of the shearing type; cats do not crush or grind their food.