The sisters are under age, and are not working. So they do not have any income. 

In the family, the oldest son has income of about 8000, and the parent got an income about 10000. The parents will file the return and claim the kids. The oldest son, supported two of his siblings (sisters) during 2019, so CAN he file for head of household and claim the two siblings as dependent? 

So the question really is, Despite parents who can claim all the children as their dependent, can a sibling claim one or two of the children?

Which basically means can the parent and the oldest son split the the 6 kids between each other? Say parent claim 4 kids, and the oldest son claim 2 kids. Or just the parent have the right to claim them, and the oldest son CAN NOT?