That sounds like a lot to me - my cat goes through about 2-3 pouches when he's not on his normal food (raw meat).
Then again, he is fed high quality wet food - which Felix isn't. Because Felix has less nutritional value, they need to eat more to get enough nutrition than what they would have to eat if they had a better quality food. That's probably why yours are eating so much, but I'd suggest you take them to the vet to ensure there's nothing wrong with them, just in case.
Then, once the vet has confirmed they're fine, I suggest you change the food to a higher quality - I recommend Hi Life pouches, they cost £4.99 for a pack of 12 and are sold at Tesco/Waitrose, etc.
Remember when you switch them over to do it gradually by mixing a little in with the Felix and slowly increase the amount of the new food, over about a week. Also don't stock up on any new food until the cats have tried it and approved
Just out of interest I have added the ingredient lists for Felix as good as it looks Tuna version, and Hi Life Tuna & Salmon version:
Felix:
Meat and animal derivatives, vegetable protein extract, fish and fish derivatives (of which tuna 4%), minerals, various sugars.
Hi Life:
Dolphin-friendly Tuna (min. 55%), Alaskan Salmon (min. 5%), Sunflower Oil, Vitamin & Mineral Supplements, Tapioca.
Interestingly, the Felix tuna version contains mostly meat/derivatives, and only 4% tuna - while the Hi Life version contains a huge 60% tuna/salmon and no meat.
Felix also uses fish and meat derivatives, which are all the disgusting bits on the animals that have little nutritional value - think hooves. None of that in Hi Life.
Felix also has added sugars - not good for the cat's teeth!
All in all, Hi Life is a much better food, and only slightly more expensive. And, if I'm right, you won't spend much more anyway because they'll be eating less - so I guess you're even when it comes to money but up when it comes to your cats' health, which can only be a good thing
Best of luck!