We generally cannot prove things about physics in a mathematical sense, but assuming that our understanding of quantum mechanics is correct, every interaction of an entangled particle causes its entanglement to "spread" to the interacting object. That's just a property of the math involved in describing quantum systems.

This means that once you have macroscopic interaction, the entanglement basically starts to spread at the speed of light, i.e. it'll quickly spread to humans.

Once you are entangled with something, you can no longer observe the effects of that entanglement (you are no longer an external observer), and it looks as if the entanglement was destroyed.