It is permissible for the husband to wash his dead wife and it is permissible for the wife to wash her dead husband. The Prophet’s daughter, Fatimah, left instructions that `Ali should wash her.

The one who is most entitled to lead the funeral prayer over the deceased is the Imam of the mosque, whether or not the deceased left instructions that a particular person lead the funeral prayer over him. If the Imam of the mosque gives up that right and allows the one whom the deceased had named to lead the prayer, there is nothing wrong with that