ויאמר יוסף אל אביו בני הם אשר נתן לי אלקים בזה Rashi says הראה לו שטר אירוסין ושטר כתובה. The mefarshim say Yosef was telling Yaakov not to suspect that they weren't fit for beracha since they were not born to him from a proper marriage. But if this is the case, why didn’t Yaakov suspect this during the 17 years he had already been in Egypt? And why did Yosef need to present both a shtar kiddushin and erusin, the shtar kiddushin should suffice? The Rebbe (Likutay Sichos volume 30) explains that we don't find in the simple peshat of the pessukim that the Avos did kiddushin. Why not? For the cheftzah of kiddushin - of a marriage as a form of kinyan - is only a chiddush of the Torah. Pre-Mattan Torah the only form of marriage was through living together as a married couple. The Torah is mechadesh the concept of a binding kinyan of marriage through a kinyan. However, since Yosef was in Egypt, a place of immorality, he did the kinyan of kiddushin to demonstrate that his marriage was a binding kinyan that was not going to be broken. Hence, he had a shtar for the kiddushin as a lasting proof of his binding marriage and a shtar כתובה since that is part of the binding marriage post Matan Torah. Yosef was telenig Yaakov don't think that the fact they were born in such a terrible place should make them unfit for beracha for I erected extra safeguards that they should not be affected.
When Yosef is sent by Yaakov to look for his brothers in Vayeshev, he asks someone where they are and the person answers נסעו מזה which Rashi says means they have separated themselves from being your brother. The Sifsay Chachamim says that the word זה has gematria 12 alluding to the 12 brothers and the man was telling Yosef נסעו מזה, they have removed themselves from זה, being 12, they no longer want to be 12, they want to remove you. In light of this we can say the same idea Yosef was conveying to Yaakov. בזה, my children are proper children to descend from the 12 shevatim, they are fitting of receiving beracha like the shevatim.
