Question on Joseph's dream

While reading my daily Bible reading, including Genesis 37:5-11, it suddenly occurred to me that there is something strange about one of Joseph's dreams, or the interpretation thereof.

Joseph told his father, Jacob, that he dreamed that the sun, the moon, and eleven stars bowed down to him. Jacob asked him if his father, his mother, and his brothers would, indeed, bow down to Joseph. I must have read that thirty times, at least. Suddenly something jumped out -- Rachel, Joseph's mother, died while giving birth to Benjamin, Joseph's brother. So either he would not have had eleven brothers, because Benjamin hadn't been born yet, or he wouldn't have had his mother, or something else is going on. The only explanation I can think of, and it's not very satisfactory, is that Jacob was referring to Leah, his surviving wife (who was Rachel's sister). The NIV reference Bible suggests that solution.

The dream was more or less fulfilled, in that Joseph's brothers had to pay him homage when he was the de facto ruler of Egypt. But Jacob and Leah weren't present in Egypt at that time, and, apparently, Leah never was, as she seems to have died before the family went to Egypt. (Genesis 49:31)

Any thoughts?

Related to this subject, who acted as Benjamin's mother? How much younger was Benjamin than Joseph? Their father called both of them children of his old age.