I agree if the life estate is measured by the life of the life tenant. However, as I mentioned in my prior response, it is possible for a life estate to be measured by a life other than that of the life tenant. If, for example, the deed reads, "from O to A and his issue for the life of B, and then to R," the death of A would not terminate the life estate.
Also, in your first response, you wrote, "The life estate doesn't pass to the grandchildren, it passes to the remainder man or men, which would also be named in the will. In other words, after the brothers died there should not be a life estate." The last part of that doesn't make any sense. There's all sorts of imprecise language in the original post, but it seems to imply that the OP's sister is the life tenant and that the OP's nephews were the remaindermen. The nephews/remaindermen have died, but the sister is still alive, so why would that result in there "not be[ing] a life estate" anymore? If, in fact, the life estate is measured by the life of the OP's sister, then it is very much still in existence since the sister is still alive, with the remainder interest presumably passing to the heirs of the OP's nephews.

