Who is the legitimate heir to the questioner after her death, and is it permissible for her to bequeath her share of her father's house to her sister's son, knowing that her brother's sons have received their share and are financially well-off?

If you pass away before your four sisters, they inherit two-thirds if they are full sisters or paternal half-sisters, and one-third if they are maternal half-sisters. Your nephew also inherits as a residuary heir ('asaba), taking what remains after the sisters' share. You may bequeath up to one-third of your wealth to your sister's son, and any amount exceeding one-third is not enforceable unless the heirs agree.