can my sister get custody of children 8 & 10 years - she does not earn

Incase your sister  want to seek divorce from your husband you can file divorce petition under Section 13 (1)(i)(a) of the Hindu Marriage Act 1955(assuming you are a Hindu).Further she shall be liable to get alimony / maintenance from your husband  under Section 125 CrPC as well as Section 24 of the HMA during the pendency of your Divorce proceedings. The Court shall decide the maintenance  based on the facts and circumstances.

Since her child is a minor  she is  required to file a petition for the custody of your child
 
Section 6 of The Hindu Minority and Guardianship Act states that the ‘natural guardian of a Hindu minor, in respect of the minor’s person as well as in respect of the minor’s property. In the case of a boy or unmarried girl is the father, and after him, the mother, provided that the custody of a minor who has not completed the age of five years shall ordinarily be with the mother. For appointment of declaration of any person as guardian, the court shall consider the welfare of minor. Since your child is a minor so you will only get the custody of your child.However the welfare of the child is determined neither by the economic affluence nor a deep mental or emotional concern for the well being of the child. The answer depends on the balancing of all these factors and determining what is best for the child’s total well being."