Definately way too small for these babies. I did the same thing at first too because the place I got mine from weren't very knowledgeable.
About C&C Cages - C&C Cages for Guinea Pigs
How to Make a Guinea Pig Cage - Cubes and Coroplast (C&C)
This is the way to make these cages and the size requirements. Go through the posts here when you can; there are tons of other pics to give you an idea of how these are set up. The cost is not so much and it's a lot of fun making one that you like and your babies will be very happy with. I guarantee you will have some major happy piggies when you change it.
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The first pic is what I started with after making the first one from a small cage for my two but added and embellished based on piggie preferences, etc. Anything is fine and doesn't need to be fancy, honestly. Just what can make the boys happy.