Looked at the file the problem looks like the edges that you have extruded for the hand are not kept together. Make sure you have keep faces together checked so when you extrude they will stay together. Its under polygon> tool options> keep faces together.

Also where the shoulder was connected you had some faces sticking out towards the center grid that where not merged.

I got booleans to work after I fixed them first try.

Here is the fixed file. I havent cleaned up the geo yet but the finger are together.