Well, its logical that a model file is large when you have a lot of animation frames and you have models with a really high resolution of polygons. Export your animations with at least 9 frames per cycle and basing on that time-scheme the other finite animations. Use a DDS texture to decrease the size consumpted by the texture. Splitting the model into two different ones with less consumpted space is senseless and could lead to a longer loading time and maybe issues while animating them.

There is absolutely no problem to have models with animations that make the MDLs blow up. Its absolutely ok if they are the only ones that are so big. Though, you should consider to have a look at bones animation. Maybe you can use more animations with less consumpted space with that method.