can do but post a full size picture
(I don't think it will ever be 'pretty because the background is so bright and the colors in the clothes are all over the place but it's easy enough to make it considerably better.)
The people are badly under exposed because of the bright background. Fill flash should have been used to balance the exposure of them to the background.
With the right flash unit and exposure settings the background could have been made darker than the people.
I bet the camera used Evaluative/Matrix light metering mode.
Spot metering mode and metering for the people would be another approach but he background would be solid white (blown out)
Center-weighted metering might have worked.
JPEG files have limited, if any, editing headroom.
You don't say what you are editing with. And your profile is set to Not OK to edit.
So, make 2 copies. Keep one as is. Use a white balance too to set the white reference to the tall girl, second from left. Use the white patch on her left shoulder. This copy will give reasonable skin tones but the background will be mostly yellow. Layer the copies. Mask to get the background from the unchanged copy and the people from the white balance corrected copy. It should look way better in about 5 minutes.