My twin girls weigh 20 lbs. and are 28 inches long. This is what they eat
3 tablespoons of cereal twice a day with a sm. Jar of fruit and a 6 oz bottle
A sm. Jar of veggies with a 8 oz. bottle once a day
And an 8 oz. bottle at bedtime
And a couple oz. of juice mixed with water once a day

Is this too much or too little for their age and size?

You don't say out old your girls are? An important part. I don't know about the diet, not knowing the age but they could be getting more water per day without the juice.
What is the 8oz. Bottle, formula ?
Tick

My girls are 6 months old

I'm sorry the girls are 6 months old. And yes the 8oz bottle is formula