What is the ruling on the paternal uncle's daughter spending the night at the house of the questioner's father if the corridors are shared and there is a fear of seeing her without a hijab, knowing that the questioner is 15 years old?

The matter is as you have read regarding the impermissibility of cohabitation between non-mahram individuals if the facilities or passages are shared. However, if the situation is merely a visit from your cousin to your family, we hope there is no harm in her presence in the house, provided that Islamic guidelines are observed, such as avoiding private seclusion and seeking permission before entering or passing through a place where she is present, so that no non-mahram men see her without full hijab. If something like that happens unintentionally, there is no blame upon you, for Allah Almighty said: "Our Lord, do not take us to task if we forget or make a mistake."