Why does the Torah write that Moshe "rode 'his wife and sons on the donkey"'? Which donkey?
Rashi: This is a special donkey - the same donkey on which Avraham rode to the Akeidah and on which Mashi'ach will be riding when he will reveal himself to Yisrael.
Seeing as at this point, only Gershon was already born (See above, Shemos 2:22), why does the Torah write that he took his sons?
Ramban #1: The Torah sometimes refers to a single person in the plural. 1
Ramban #2: Eliezer was born the moment he returned to Midyan. He neither circumcised him nor gave him a name at that stage, because he was busy with Hashem's command to go to Egypt on his special mission. 2
Targum Yonasan: Refer to 4:24:2:3*.
Ramban: See for example, Pinchas, Bamidbar 26:8. Tziporah must have either become pregnant with Eliezer on the way to Egypt, or in Egypt, assuming that Moshe took her there.
And it was only when he arrived in Egypt and saw that he had been saved from all those who sought his soul that he appropriately called him Eliezer (Ramban).
Why does the Torah mention that Moshe took the staff after writing that he returned to Egypt?
Rashi: To be sure, he took the stick before leaving for Egypt, only the Torah does not always follow the chronological order.
Seforno: The beginning of the Pasuk is referring to Moshe's returning to Yisro from the desert; 1 And the Pasuk then tells us that, after depositing his wife and children with his father-in-law, he returned alone to Egypt, having taken his staff with him. 2
If Moshe took his wife and sons with him to Egypt, as the Pasuk implies, how is it that, at the beginning of Yisro, Yisro brought them to Moshe from Midyan?
Rashi (in Yisro): When Aharon met Moshe at Har Sinai he questioned the wisdom of taking his wife and children to Egypt, so Moshe sent them back. 1
Ramban #2 (citing the Ibn Ezra): Initially, Moshe did indeed take Tziporah and his sons with him. However, when the incident recorded shortly after (Shemos 4:24-26) occurred, it was not possible for them to continue to travel, so, not wanting to delay fulfilling Hashem's command, he left them in the inn with instructions, that, when Eliezer will have recovered, they should return to Midyan. 2
Seforno: Refer to 4:20:3:2.
In fact, Yisro advised Moshe to leave them in Midyan, but Moshe insisted on taking them with him - so that they should not miss Ma'amad Har Sinai. Yisro conceded to Moshe, and Hashem corroborating Moshe's decision, ordered him to return to Egypt with his wife and children (Ramban citing the Midrash).
Why does the Torah not mention the birth of Moshe's sons, and the reasons for their names here (only in Yisro, Shemos 18:3 & 4)?
Ramban #1: In fact, in spite of the term "Banav", only Gershom was born, and Tziporah became pregnant with Eliezer on the way to Egypt or in Egypt, assuming that she actually went there. 1
Ramban #2: Although Tziporah was pregnant with Eliezer, he was born only after Hashem spoke to him by the Burning Bush. And because Hashem's command was incumbent upon him, he did not circumcise him before departing for Egypt; nor did he manage to name him after circumcising him due to the incident with the angel. And it was only after he arrived in Egypt and discovered that he was no longer threatened by those who sought his Soul that he named him Eliezer - "Because the G-d of my father assisted me ... ."