Is the fiancé obligated to spend on his fiancée’s house and her family after her father’s death, or is he only required to spend on his fiancée?

There is no obligation to spend on the aforementioned household members or the fiancée's expenses. Rather, the wife's maintenance becomes obligatory after consummation of the marriage (Dukhool) or her surrender of herself (tasleem al-nafs), and the maintenance of poor parents and poor children who have no wealth. As for those other than them, their maintenance is not obligatory. However, it is recommended to spend on and show kindness to relatives, especially if the one spending has wealth, and there is a great reward in it if one intends the reward and strengthening kinship ties.