Hello, I am just wondering how i can attach the two head pieces
whenever i try to attach the seperate head piece (to the right) it attaches to a shoulder or something
how do i attach the seperate head piece to the actual head

If you are selecting all of the edges around the seam and then welding, select one less edge then weld. Then weld that last remaining edge.

I'm not really sure which edges attach to what so its kind of hard to tell what's going on...

When stitching 1 to 2, sometimes you need to stitch 2 to 1. <---(Ancient proverb? LoL)

If that doesn't work you can target weld the points, but that's a lot more clicking.