Hi there!
Firstly, I have to say that I love that you are doing this! It's such a thoughtful present!
I would love to undertake this project, as this is the area of illustration in which I usually work and deliver the most satisfaction to my clients. I primarily create images of couples for either wedding gifts or life events, or occasionally stationary pertaining to either. I work in a cel-shaded graphic comic-book style ordinarily which is well-suited to adaptation to the style of the Ninja Turtles, or I can render it in my more usual style, of which you can see a few examples in my portfolio on here. If you message me I can send you additional examples, if you like what you see.
I work by inking by hand then scanning the image and colouring it in Photoshop, and can easily make colour tweaks on request once you view it. Please let me know if you've any questions, you can discuss it hypothetically with me without accepting my offer. But I am interested how close this is to my usual work and believe I could do a really great job!
Take care and have a great weekend
Regards
Laura