Section 2 of the Employees state insurance Act deals with the definition of family which is as follows
Section 2( 10): Family means all or any of the following relatives of an insured person, namely :
(i) a spouse ;
(ii) a minor legitimate or adopted child dependent upon the insured person ;
(iii) a child who is wholly dependent on the earnings of the insured person and who is
(a) receiving education, till he or she attains the age of twenty-one years,
(b) an unmarried daughter
(iv) a child who is infirm by reason of any physical or mental abnormality or injury and is wholly dependent on the earnings of the insured person, so long as the infirmity continues ;
(v) dependant parents, whose income from all sources does not exceed such income as may be prescribed by the Central Government ;
(vi) in case the insured person is unmarried and his or her parents are not alive, a minor brother or sister wholly dependant upon the earnings of the insured person
In these definition the Grand Mother and Grand Father is not included , hence they are not eligible for the ESIC benefits.
But as per 2 (10) (vi) the Dependent minor sisters or minor brothers will get the benefits if the insured persons father and mother is not alive.