When Did Yaakov Bless Ephraim and Menashe?

Introduction

Adults or Youths?

In Bereshit 48, Yaakov gives Yosef's children tribal status and blesses them.  The placement of the narrative a few verses after the statement "וַיִּקְרְבוּ יְמֵי יִשְׂרָאֵל לָמוּת"‎¹ and just a chapter before his actual death suggests that the event is taking place towards the end of Yaakov's life.  The fact that the story opens with Yaakov on a sickbed and ends with his telling Yosef that he is soon to die, would seem to confirm this.  Several aspects of the story, nonetheless, make one question the chronology:

• "מִי אֵלֶּה" – Upon noticing Yosef's sons in verse 8, Yaakov asks "who are these?" as if he had never met them before.  If the story is taking place seventeen years after Yaakov's arrival in Egypt,² how is it that Yaakov does not recognize his grandchildren?
• "רְאֹה פָנֶיךָ לֹא פִלָּלְתִּי וְהִנֵּה הֶרְאָה אֹתִי אֱ-לֹהִים גַּם אֶת זַרְעֶךָ" – These words seem to suggest that Yaakov is seeing his grandchildren for the first time and that it is only recently that he has had the opportunity to reunite with Yosef. If the two families had been interacting for years, why express such emotion?
• "וַיּוֹצֵא יוֹסֵף אֹתָם מֵעִם בִּרְכָּיו" – Before Yaakov blesses Menashe and Ephraim, we are told that Yosef took them out from between his thighs.  The image that is evoked is of two little boys emerging from his lap.  Yet, if Yaakov is near death, Ephraim and Menashe should be in their early twenties, not young children.³

How are the contradictory verses to be reconciled?  Was Yaakov near death and his grandchildren already adults during the episode, or did the story take place close to Yaakov's arrival in Egypt when Yosef's sons were much younger?