When did Moshe send Yisro away?
Why did Yisro leave Yisrael?
Rashi and Targum Yonasan: In order to convert his family (all the people of his country - Targum Yonasan). 1
Seforno: Refer to 18:27:3:2.
Mechilta: Refer to 18:27:3:3.
Refer to 18:13:2:1**. According to the Mechilta. Refer to 18:5:0.1:2, he went to convert his wider family and country, since his sons came with to the desert and converted. See Oznayim la'Torah on Pasuk 27.
Why did Yisro decline to accompany them to Eretz Cana'an?
Rashi and Targum Yonasan: Refer to 18:27:2:1.
Seforno: On account of his old age. 1
Mechilta: Because he considered it inappropriate 2 for a Ger to travel together with Yisrael (Refer to 18:27:1:2*). 3
Like Barzilai ha'Gil'adi in the time of David ha'Melech in Shmuel 2, 19:38 (Seforno). Yisro's sons however, did accompany Yisrael to Eretz Cana'an - as is evident in Seifer Shoftim (1:16).
Though this is difficult to understand, bearing in mind the large contingent of Eirev Rav that accompanied them out of Egypt.
Refer to 18:27:1:2*,