Sheikh Ahmad al-Khalîl, professor at al-Imâm University, Qasîm Branch
If a woman handles the washing of her deceased husband, the relatives who should help her are the husband’s father or his sons. It is also permissible for other men who are mahram to her to help her.
Other women may not participate in washing, no matter how closely relative they were to the deceased. Women are not allowed to wash other than their own husbands.
The basic rule is that men should be washed by men and women by women with the exception of the husband and wife who are allowed to wash each other. For a deceased boy or girl who is seven years old or younger, it is allowed for either men or women to wash them.
Source: Islam Today