Do you think they don't already share the same skeleton? Haven't you noticed that sometimes the lizard's tail looks a bit weird because they're using human animations, which weren't designed for a tail?
They all have two arms and two legs. The lizards also have a tail which you need to account for but that only adds a little extra complexity.
For the most part, when it comes to chest and leg armour, it's a matter of connecting it to the universal skeleton, and applying the relevant morphing rules to make it match the body shape and animations of the specific body type.
Lizards would need unique boots and possibly also gloves. Of course, many of the races may also need unique helmets, but this limits the amount of extra work you need to do just because one race has a bigger chest than another one.
