It's hard to see exactly what happens there. I can say that a Spine skeleton is made up of many images. When you draw, they will be blended with the background, but they will also blend on top of each other. If you want your whole skeleton to be translucent, making the images translucent won't be sufficient unless you draw only one image. When you draw the second translucent image on top, it will be blended with the first where they overlap.
What you can do is render your skeleton to a texture (an FBO aka frame buffer object), then render the resulting texture with alpha. Since the resulting texture is just one image, the entire thing can be drawn translucent.
This is a common approach taken for blending particles. You want the particles to blend with each other additively, but then you want to draw the result with normal blending on top of your game. If you draw the particles additively on top of your game and the background is a light color, the particles blended with the background will be mostly white.
You might want to use premultiplied alpha images. I'm not sure if this would help your problem though.