For some inexplicable reason, the number "five" is a recurring theme in the story of Joseph. Here is a sample:
Gen 41:34 - Let Pharaoh appoint commissioners over the land to take a fifth of the harvest of Egypt during the seven years of abundance.
Gen 43:34 - When portions were served to them from Joseph's table, Benjamin's portion was five times ...
The same Joseph also did the following 5's.
When portions were served to them from Joseph's table, Benjamin's portion was five times as much as anyone else's. So they feasted and drank freely with him.
To each of them he gave new clothing, but to Benjamin he gave three hundred shekels of silver and five sets of clothes.
The difference is rather simple - the total family of Jacob was 70 people.
Joseph had two children + Jacob himself were obviously four people. Therefore, we have:
(a) 66 people other than Joseph's family and Jacob + (b) four people of Joseph's family + Jacob = 70 people in total.
Note the difference in the carefully worded sentences:
(a) all the people who ...
As explained by @Frank Luke, the original Jewish audience for Matthew would immediately have connected the number 14 to David. This was anticipated in verse 1 where Jesus is introduced as the "Son of David". It is crucial for Matthew to underscore that Jesus was the Messiah=Son of David. Of course, "son" is here used in an extended, ...