Hi m!
First truth of "fitness" - you can't spot reduce. Especially with abs - its all about the diet! In in my completely non-doctor opinion, you are definitely going to have some challenges after 3 c-sections - I don't know what impact that has had on the muscles of your abs. The tummy tuck will definitely help, but its all about the diet. Working abs every day will do 2 things - it may actually make you more "square" in the waist area because you are building those muscles with all the training, and secondly, you aren't giving those muscles a day off. Your abs are a muscle group just like your bis/tris, quads/hams, etc. You don't train those every day - at the very least, each muscle group should have at least 24-48 hrs of recovery time.
Another thing you can always do if you can't get a certain body part to completely respond the way you want, you can always build other body parts to create the ILLUSION of a smaller other part - for ex, some people are just not built with a small waist or tushie - so you can focus on building a broader upper back / shoulders to create a greater "V" shape from top to bottom.
Back to the diet, what is your current diet & stats?