The simplest explanation is there’s no one else.
And you wouldn’t want to meet them if there were.
False. Both sentences.
It is suspected, and almost proved, that organic life (plants and animals from viruses to humans) started from inorganic stuff. The process may repeat itself in the future or maybe it already happened and we haven't noticed.
The life we know is based on carbon.
There may exist other kind of lives that are not based on carbon or the carbon based population might have resources like water and oxygen in abundance.
Even the theory of negative spin antimatter seems to be more fantasy than science fiction. So I would not worry about it.