The total number of Jacob's descendants was 70; Joseph was already in Egypt.
References for Exodus 1:5
Then Joseph and all his brothers and all that generation died.
But the Israelites were fruitful, increased rapidly, multiplied, and became extremely numerous so that the land was filled with them.
References for Exodus 1:7
A new king, who had not known Joseph, came to power in Egypt.
He said to his people, "Look, the Israelite people are more numerous and powerful than we are.
Let us deal shrewdly with them; otherwise they will multiply [further], and if war breaks out, they may join our enemies, fight against us, and leave the country."
So the Egyptians assigned taskmasters over the Israelites to oppress them with forced labor. They built Pithom and Rameses as supply cities for Pharaoh.
References for Exodus 1:11
But the more they oppressed them, the more they multiplied and spread so that the Egyptians came to dread the Israelites.
References for Exodus 1:12
They worked the Israelites ruthlessly
and made their lives bitter with difficult labor in brick and mortar, and in all kinds of fieldwork. They ruthlessly imposed all this work on them.
Then the king of Egypt said to the Hebrew midwives, one of whom was named Shiphrah and the other Puah,