the head is not blended with the rest of the image.

The head is a bit "greenish" in tone, compared with the rest of the image. Perhaps a warming filter at a low opacity would help it blend better.

When were renaissance paintings ever monochromatic? Who put Brad's head in a vise?

Angelina's face is too shiny - i guess - try more adjustments like brightness maybe ?

good luck

This looks very rushed and sloppy.
Angelina's face is too far down on the head and way too high contrast.
Brad's face is HUGE on the baby's head, and is terribly distorted, with too much shine on his cheeks an forehead.
The monochrome just looks boring, and really accents the lack of matching texture where you've pasted the faces on...

Needs a lot more work.

so funny.....

Please post source links.

Sources added ! thank you

the face especially on the bottom seems a bit to stuck on -- maybe some warping or dodging would improve this

Thank you sir , i guess i fixed it now !

The shading of Shatner's face is just a wee bit too light, both the features and the shadows on the side of the nose. Perhaps just a bit Burn Tool, or Brightness and contrast adjust to the center of the face would make it blend better.

He actually resembles the woman, somewhat. Good choice of painting!

Thanks for your advice Mossy...appreciated.