When Joseph's brothers came to Egypt, did they recognize Joseph?

No, Joseph's brothers did not recognize him when they first came to Egypt to buy grain. Scripture records that Joseph immediately knew who they were, but they did not know him. This illustrates Israel's failure to recognize Christ at His first coming.

Les explains that when Joseph's ten brothers came down to Egypt to buy corn, Joseph knew his brethren just as soon as they stepped into his environment, but they did not know him. Les draws the analogy to Christ at His first coming: the Lord knew Israel from their very beginning and presented Himself in language clear as day, but they never recognized Him. This is exactly the lesson Stephen is driving home—just like Joseph's brethren came and were recognized by Joseph, but they didn't know Joseph. The brothers later returned a second time to refill their sacks with grain, as recorded in chapter 45.

Genesis 42:8

And Joseph knew his brethren, but they knew not him.

Did Joseph recognize his brothers when they came before him in Egypt?

Yes. Joseph knew his brothers as soon as the ten men came before him in Egypt; he immediately recognized who they were. They, however, did not know or recognize Joseph. The account presents this contrast as a picture of Christ's first coming, when the Lord knew Israel, but they did not recognize Him.