Answer 3, sort of:
This answer may differ in community property states. I'm not in one or near one, so won't provide that here. In equitable distribution states-
Decedent's share of property that is inherited gets stepped up, existing accumulated depreciation is wiped out, and depreciable life starts over at 27.5 years residential, or the 39 years for commercial. This also means there is no recapture.
For the 50% portion of the property that already belonged to the survivor, that basis remains intact as does the 50% share of depreciation and its remaining depreciable life. This means that the overall depreciation of the entire property is calculated in two halves. It's like having two separate assets to depreciate.
Other things about this situation: If the property has carryover losses, both halves are available for use in the year of death. In subsequent years, only the surviving party's share of the loss carryover will remain. In other words, the decedent's 50% share of the loss carryover dies with the death, but is available for use in the year of death, the same as how capital loss carryovers work for a married couple.