Grab a flatbed scanner and start scanning the books. A phone camera can be used for text, but it needs to be at least 16mp for 8.5x11 pages, adding glass to hold the pages flat. A computer sound card is enough to record the tapes. If the sister took books or tapes, ask to borrow them to copy if you can ever get ahold of her. Offer her digital copies of what I just mentioned if it might help grease the wheels.