Hi Ladies, 
I had my c-section 10w ago after a twin pg, carried almost to term 36+w (term is 38 for twins). Today I went for a fitness evaluation, and I couldn't do even 1 sit-up. It wasn't like I couldn't do it because it was sore, or my muscles burned....I couldn't do one like I was missing muscles in my abs. I wasn't able to raise my body even an inch off the ground. I wasn't in the best shape pre-pg...but I'm sure I could have done at least 1 sit-up, or even a 1/2 at that. It was like a bird trying to fly with no wings, could not even get off the ground.
is this normal? Aside from that, I think I'm pretty much healed up. My incision doesn't hurt, every once in awhile I feel stinging if something rubs there...and my skin is numb from the belly-button down.
Are you all able to do sit-ups? 
Re: No Ab muscles at all?
Have you had a doctor or physical therapist see if you might have diastasis recti? It's when your abdominal muscles separate, which is a possibility if you've just had twins. I have some from my second son (he was 10.5 lbs at birth), and have been going to a physcial therapist who deal specifically with it. The exercises are easy, and I think it's really been making a difference.
https://en.wikipedia.org/wiki/Diastasis_recti
https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002569/
DS2 - Oct 2010 (my VBAC baby!)
I 2nd the post on diastasis. YOur separation may be pretty severe. I had this. My LO was 9.13 lbs when he was born and I'm a petite person.
I got the muscle repaired along with a tummy tuck. The scar isn't nearly as pretty as it was from a c-section, but my buldge on the upper abdomen is almost gone.
The way I knew I had diastasis recti was when I would lay flat and use my stomach mucles to try to sit up my stomach would form a tent down the middle. This is what it was like while I was pregnant so I am not sure if there is a difference while you are not pregnant though. My muscles just automatically went back together, thank god.
You can go online and find some really good exercises though and see if that helps.
On this blog there is a picture of the "tent" I am talking about
https://melissamcfarlin.blogspot.com/2010/05/diastasis-recti.html