Core questions

I'm really struggling with strengthening my core! I love the new workouts, and the new core exercises...but find that I simply cannot do a lot of them. I have had 2 C-section deliveries, and a total of 7 pregnancies. So, I know I've put my abdomen through a lot!

However, my youngest is 7 years old now, and I've been working out with FB for 5 years now. I've come a very long way from where I was 5 years ago (thanks to all the Pilates videos and fantastic programs here!), but am feeling discouraged at what I still can't do (boat poses, V-ups, full sit ups, Russian twists with feet elevated, etc...).

I'm wondering if this is just how my core is now or if it can still improve.

Any insights or advice would be much appreciated! Thank you!