Grey, purple and pink... Somewhere I hear a designer turning over in his grave!

When doing work of this nature, the pre-shoot consult is essential. Clients rarely consider choices in clothing style or colour and as the expert, your input is critical to delivering a final, polished product.
Looking at the image in detail, a points jump out at me. First of all, Dad is nearly invisible, except for his arms, which look like they belong to Mom, and she looks like she has grey sleeves....
My approach would have been to have Mom turn a little more to her right. Not a lot, but just enough to profile her pregnancy, then have Dad shift a little too his left, and have her arms on the outside, under his. This does two things, it clearly shows both of their arms, and it also shows her wedding ring (if one is worn).
As far as the colours go, since the pink of the shoes is obviously critical, I would have suggest a darker green for one parent and a blue for the other. Muted tones of similar value will provide the greatest contrast with the pink without clashing as well as allow for a clear separation between the two sets of arms.