Can I get a snatched waist and big butt? I am a 27 years old female and have 3 kids. (photos)

Hello and Great Question. I appreciate the time you are spending researching this procedure. My name is Dr. Matthew J. Nykiel. I am a Board Certified Plastic Surgeon, a Fellowship Trained Cosmetic Surgeon, and a Butt Augmentation Specialist.
Based off your photos you would be a great candidate for a BBL which would consist of lipo 360 and a fat transfer to your hips/butt giving you more of an hourglass figure.In regards to the tummy tuck you would need to be seen in person. I would definitely recommend doing an in person consultation with a board certified plastic surgeon who specializes in this procedure and who can suggest what is needed. 
I hope that helps! Best of 
Luck! 
Matthew J. Nykiel MD

BBL and tummy tuck can be performed either way.  There may be strategic advantage in some patients with a little more subcutaneous tissue to delaying the tummy tuck.  This really needs to be determined by an exam by a board certified plastic surgeon.  Six months later you could have the TT to address skin laxity.To achieve the smallest waist possible and the best waist to hip ratio, I would recommend lipo of the back, abdomen, flanks, and love handles with fat transfer to the buttocks. If the waist was smaller at one time, the waist can likely be reduced to those same measurements or smaller provided the muscular and fascial integrity has remained the same.  

Thanks for the question. 
In this regard, I recommend you waist and back Liposculpture, getting better curves especially in the waist, improving your body contour.
Finally, I suggested take the fat we get and transfer to the buttocks and hips, to mold them and get better volume, contour and butt projection, is that we know as "Brazilian Butt Lift" (BBL).Kind regards