Gertie and Ida are eating more than both Linus and Truman, so I wouldn't increase their intake unless you notice there is a problem, which it doesn't sound like there is.
Dog food bags notoriously recommend overfeeding the dog, of course, so you have to buy more food. Bulldogs aren't incredibly active most of the time and get fat super easy (and it's NOT easy to get off) so I would err on the side of caution in feeding.
For reference, I feed Truman - 8 months old - one cup of dry food twice a day, with a little wet puppy food on top in the morning only. He weighs 47 pounds and the vet said he is very healthy and at an optimal weight for his breed and size right now. He is also a piggy when he eats, I think it's a bully thing!