Well you could go right back to basics.
Load them all into Photoshop as a stack. You could try to see if Photoshop can align them , but I doubt it will - the bit you want to align is so small compared to the background
.
Zoom in to about 400%, and turn all the images off except the bottom one of the stack. Turn the second bottom one on and make it 50% opaque, then drag it till it lines up on the bottom image. Repeat this with each successive image in the stack.
When you have them aligned, adjust the opacity of each image from the bottom to 1/n opacity e.g. 100%, 50%, 33%, 25%, 20%, 17%, etc. this will ensure each image contributes the same amount to the final stacked image.
Have fun!
Al.