Animating bones and the entire skeleton together

Hello. I have a character with a skeleton, rigged and skinned. I have an animation of walking. I also need a animation for my hands, so I have two animations with keyframes o*n hands only*. Also walking animation doesn't contain keyframes for hands. I need to play animation for legs and hands at the same time. I tried AddMixingTransform from official guides, but it doesn't work. I tried Crossfade, it doesn't work either. How can I animate it?