1) The toy has been left by somebody in the years.
2) Mistakes were made by them in the test.
3) A big parcel was sent by her uncle to her for her birthday.
4) Old things are kept by them in the cellar.
5) Why hasn't the bathroom been cleaned yet?
6) His flat was sold by them for the debts.
7) The party hasn't been organized by them properly.
8) A new doll will be bought by then for their daughter's birthday.