Yaakov famously blesses Ephraim and Menashe but who tells Yosef to bring them to their grandfather? It doesn't seem that this would be a natural thing to do as they are not Yaakov's sons. Does someone tell Yosef to do this?
Midrash Hagadol (to Gen. 48:1) cites an opinion that Osnas, Yosef's wife, urged him to do so: "I have heard that anyone who receives a blessing from a tzaddik is as if he received it from the Divine Presence. Take your sons so that he can bless them!"
Rav Meir Eliyahu says that it is good to a get a Beracha from a Sadik before they die.
RaSh"I, commenting on Bereshit 48:1, states:
ויאמר ליוסף: אחד מן המגידים, והרי זה מקרא קצר. ויש אומרים אפרים היה רגיל לפני יעקב בתלמוד, וכשחלה יעקב בארץ גושן, הלך אפרים אצל אביו למצרים והגיד לו
That [someone] said to Joseph: One of the tellers, and this is an elliptical verse. Some say, however, that Ephraim was accustomed to study with Jacob, and when Jacob became ill in the land of Goshen, Ephraim went to his father to Egypt to tell him.
The opinion of the "יש אומרים" answers the question of "who".
ויקח את שני בניו עמו: כדי שיברכם יעקב לפני מותו
So he took his two sons with him: so that Jacob should bless them before his death.
This answers the question of "why".