Ask the friend to give you the stash in bunches so that you can deal with it in smaller groups. You honestly can't fit that much into the family room where you are staying, so you don't want it hanging out there more than a few days. Then pack up what YOU want, bring to storage unit and bring the other stuff immediately to where you plan to donate it. Plan ahead who you will give the excess to so you aren't holding the bag as it were.