I'm not too sure about the first one, but it may just mean that Lisa sort of sunk into the chair because it was so big, and the fabric just bulged out over her body a bit. The personfication is that it's saying that the chair is wrapping it's arms around her, as though it were deliberate. As for the second quote, it sounds like the stairs are creaking as Philip and the heavy boxes weigh on them going up, so the stairs are being personified as groaning the way a human would.
