My condolences for the other cat, but don't rely on that cat to provide milk! There is a small chance she will adapt and bond with the kittens in time to provide them milk, but definitely not something chance enough to risk their lives on. Even mothers sometimes have trouble bonding and producing enough milk, much less a strange female. Call your vet and ask about formula in the meantime. If you want to encourage lactation, provide a pleasant comforting area that your cat enjoys (that is also safe for the kittens and introduce them gently to her as she rests. Be careful to always be present and keep them safe in case she rejects them. If she licks them and seems content to let them false nurse, leave them be for a while and let things come as they may. Even if she accepts them, lactation is not guaranteed. It is a good idea to get them a surrogate mother though, so try anyway.
Very sorry about the loss of your cat, I really love ours and it is always terrible when a beloved pet dies.
I agree with peach_bug. I have had a cat take over for another cat before, but she happened to have some kittens nursing already. Unless the cat has a VERY strong maternal instinct and is lactating, she is unlikely to be a surrogate. But you never know. The same cat that acted as a surrogate for our other cats kittens, also acted as a milk mother for a baby potbelly pig we had.
The other adult female can not nurse them because the babies didn't come out of her body. They came out the other cat. And I think when a cat is pregnant they are producing milk for there babies when they are born so I don't think the other cat can nurse them