Are the deceased's sons permitted to attend their mother's washing when her daughters and female relatives are present?

If the children's presence at their mother's washing means they are directly performing the washing, then this is not permissible if there are women present, because a woman's washing may only be directly performed by women. However, if their presence is near the washing area, and they are covered, with the intention of instructing those supervising the washing or similar, then there is no harm in it.