So sorry to hear this, unfortunately it happens all the time. I agree with Ly, definitely try to get the penis to express. It's really easy to do. You should be able to feel the shaft under the skin. If you haven't looked already, here is an excellent link to try and help.
http://www.cavyspirit.com/sexing.htm
I'm afraid I can't help you with the decisions you have at hand if they both turn out to be pregnant. Only you know what you can handle, but you do also need to think about what you are going to do with oatmeal. Are you willing to have him neutered so he can be with the girls, or is there a chance maybe if one of the babies are male, that they can have a cage of their own as well?