Natural Photo Integration

I need assistance placing my dad into an existing indoor picture. He should be standing in the photo. The original picture has mixed lighting.

Requirements:
- Seamless integration of the new subject
- Matching of lighting and shadows
- Maintaining the natural look and feel of the photo

Ideal Skills and Experience:
- Proficient in photo editing software (Photoshop, GIMP, etc.)
- Strong understanding of lighting and shadows
- Experience with composite images