Both our parents have attained Paramapadam. Our elder brother was performing their rites. As he has attained Paramapadam, can we sisters perform annual shraddham for our parents? As our late elder brother was a bachelor, as his siblings, are we allowed to perform his shraddham? For a spinster/unmarried woman who does not have parents, who are allowed to perform her last rites?

As your elder brother has attained Paramapadam, there is nothing that you can do for your parents; he was the kartA. The performance of rites ends with him and no shraddham need to be performed.

As your elder brother have no other relations who can perform his shraddham, as his siblings you can perform shraddham; qualified males can perform the shraddham by accepting kaippul (darbha grass) from the sisters (females).

For a spinster without parents, last rites can be performed by her siblings. If none are available, others can perform her rites.