We co signed an apartment lease for our two daughters after six months they could not afford the rent they gave a 60 day notice which we also signed as per the apartment management.
After two weeks my daughters revoked the 60 day notice.
Management wanted us to sign the revoke notice but we said no as we knew our daughters could not afford the rent.
After many calls to the apartment complex they told us that it was at will that they could stay in the apartment and all though we did not sign the revoked 60 day notice we were still liable for the rent and would still be the co signer is this a true statement ?

Law depends on the terms of each of the contracts you signed, and also on where you live. I think you will find that the contracts were written to include liability for the full term of the original lease, regardless of any notice to break it. Notice to break it, and acceptance of that, just meant that the owners can show the apartment and rent it to someone else, and most states don't allow collection of old rents once new tenants are established. But if it doesn't get rented, the original lease applies.
You got into this and now really do need to work on a way to deal with it, with your daughters and the landlord.

This is a hard one. Without seeing the wording of the lease and knowing what local laws apply, we can't really give a definitive answer. It could go either way. The 60 day notice could be considered a legal document, that, once accepted by the management, released you from liability. Or they could just say that as long as your daughters occupy the apartment under the original lease, then you are responsible as co-signers. If it comes down to court a judge could go either way and I think you need a local real estate attorney, familiar with the local laws and courts, to advise you which way it could go.