What is the expiation for taking lost money during Hajj with the intention of returning it but being unable to do so, and for taking money from a friend and being unable to repay it? Is one fidya required for both mistakes, or two?

The money you found in the Haram falls under the rulings of lost property (Luqata). The predominant view is that it is like any other lost item, and it has two scenarios: 1. If it is a small amount that its owner would not typically ask about: You may take it and own it. 2. If it is a large amount that its owner would typically ask about: You must announce it for a year in the Haram, or hand it over to the authority responsible for lost items there. If you travel with it, it suffices to send it with a trustworthy person to hand it over to those authorities.

As for the money you took from your friend and are unable to meet him, its ruling is referred to in Fatwa No. 59330.

As for the fidyah (expiatory ransom): It has no relation to the issue of money. Rather, it is specific to someone who commits an act that necessitates it during the state of ihram for Hajj or Umrah, such as applying perfume, wearing tailored clothes, or cutting hair.