Is it permissible for the wife of a recently deceased grandfather to reside in the house of her husband's children (paternal uncles and aunts), or must she return to the house of her children from a previous marriage after her 'iddah ends?

Your grandfather's wife must observe the 'iddah (waiting period) in his house, unless she fears harm, in which case she may move. After the 'iddah, if she is poor and her children are well-off, they are obligated to spend on her and provide her with housing. However, if she is able to spend on herself, then the children are not obligated to do so. The paternal uncle and aunt are not obligated to house their father's wife, except as a voluntary act.