What you need.

 First what you need to do is

open all your imagens if i spelled that right

next you start to arrange your photos like this.

put bom to the corner and shrink her till your in your 300s for width and 400s for hieght

then put top to the side but make sure tops head is below boms feathers  but a little to the right just a little

now click the little eye ball to hide them and now we move to textures

set them like this but make sure to cut the black in the birds texture and streach it out.

now go to colors and select desaturate and choose the first one for all the photos including bom and top

now we are going to stat blending go to eraser and choose 17.7 for opacity and size 145.30 for the size the brush is the one that you get when you first open gimp

start blending top and bom make it look like this

now we move on to the the back start blending the bird scene like this

same opacity and size i am just having typos but who cares!!

it should turn in like this and if you wanna add a text you can in side between bom and top I didn't add a text but if you want you can.

show me your results!!! Or what else do you want me to make :)