Seamlessly Merge Two Photos

I have a group photo and a separate portrait of one person that I need composited into a single, believable scene. The goal is seamless blending—skin tones, lighting, shadows, and overall sharpness should match so no one can tell the images were shot separately. Please keep the original background intact and position the added person wherever the composition feels most natural; I’m flexible on exact placement as long as it looks right.

When you’re done, I’d like:
• A high-resolution JPG or PNG ready for print and social media
• The layered PSD (or equivalent) so minor future tweaks are possible

Experience with Photoshop, layer masking, and color matching is essential. A quick turnaround is appreciated.