Problem Getting a Co-Signer.?

My girlfriend and I are trying to sign onto a lease at an apartment (the apartment is already occupied, we are just taking over a portion of the lease and sharing a room) and each of us needs to have a separate lease application as well as a different co-signer applications. We have found one person willing to co-sign for us, but are having great difficulties finding another. What I would like to know is if we are able to use our one co-signer for the both of us. Or do laws generally favor having two separate cosigners? I have been having trouble contacting the property management company to just ask them, hence why I am on here. Any experiential or factual information is welcome! Thanks!