Does a brother who died after a building collapsed, and whose remaining family members died under the rubble in the Turkey earthquake, inherit, given that the order of death is unknown?

There is no inheritance between those who died in the demolition if it is not known who died first. The wealth of each of them is inherited by their living heirs.

The sister-in-law's informing that her husband did not die when the building collapsed, and that he spoke to her, does not entail that her husband inherits from his father, mother, and brothers, because it is not known that his father, mother, and brothers died before him, and that his death occurred after theirs. Even if we assume her informing that they died before him, her testimony is not accepted, because one of the impediments to accepting testimony is that the witness draws benefit for herself from her testimony, and here she benefits and draws benefit for herself.