Will an uncle be rewarded for spending on his nephews, or does Islamic law obligate him to spend on them?

Scholars have differed regarding the obligation of providing for the children of a deceased brother. However, even if it is deemed obligatory, the one who spends will not be deprived of reward and recompense. Every expenditure a servant accounts for will be rewarded. Umm Salamah asked the Prophet, peace and blessings be upon him, about her reward for spending on the children of Abu Salamah, and he replied: "Yes, you will have a reward for what you spend on them." Therefore, continue to spend on them, seeking reward from Allah, for Allah does not let the reward of the doers of good go to waste.