Genesis 35:16-18 records Benjamin's birth and Rachel's death, explaining why these two are specifically called 'Rachel's sons' here.

Genesis 30:22-24 records Joseph's birth and Rachel's prayer 'may the LORD add another son' — the two sons listed here fulfill that hope.

In Genesis 30:24, Rachel names Joseph with hope for another son — that hope is fulfilled with Benjamin in 35:24's list.

Genesis 46:19-22 expands this — listing Joseph's and Benjamin's sons and grandsons who went to Egypt with Jacob.