Who sells Yosef? Who brings him to Egypt?

Question

Who sold Yosef to the Yishmaelim, is it the brothers or the Midyanim?

And who sold him to Potifar in Egypt? The Yishmaelim or the Midyanim?

(Medanim also appear in the text, but that might be the Midyanim.)

Do these texts show that the Torah is indeed a composite document from multiple sources?

Bereishit 37:27-28:

כז לְכוּ וְנִמְכְּרֶנּוּ לַיִּשְׁמְעֵאלִים, וְיָדֵנוּ אַל-תְּהִי-בוֹ, כִּי-אָחִינוּ בְשָׂרֵנוּ, הוּא; וַיִּשְׁמְעוּ, אֶחָיו. 27 Come, and let us sell him to the Ishmaelites, and let not our hand be upon him; for he is our brother, our flesh.' And his brethren hearkened unto him. כח וַיַּעַבְרוּ אֲנָשִׁים מִדְיָנִים סֹחֲרִים, וַיִּמְשְׁכוּ וַיַּעֲלוּ אֶת-יוֹסֵף מִן-הַבּוֹר, וַיִּמְכְּרוּ אֶת-יוֹסֵף לַיִּשְׁמְעֵאלִים, בְּעֶשְׂרִים כָּסֶף; וַיָּבִיאוּ אֶת-יוֹסֵף, מִצְרָיְמָה. 28 And there passed by Midianites, merchantmen; and they drew and lifted up Joseph out of the pit, and sold Joseph to the Ishmaelites for twenty shekels of silver. And they brought Joseph into Egypt.

From: http://www.mechon-mamre.org/p/pt/pt0137.htm

Bereishit 37:36:

לו וְהַמְּדָנִים--מָכְרוּ אֹתוֹ, אֶל-מִצְרָיִם: לְפוֹטִיפַר סְרִיס פַּרְעֹה, שַׂר הַטַּבָּחִים. {פ} 36 And the Midianites sold him into Egypt unto Potiphar, an officer of Pharaoh's, the captain of the guard. {P}

From: http://www.mechon-mamre.org/p/pt/pt0137.htm

Bereishit 39:1:

א וְיוֹסֵף, הוּרַד מִצְרָיְמָה; וַיִּקְנֵהוּ פּוֹטִיפַר סְרִיס פַּרְעֹה שַׂר הַטַּבָּחִים, אִישׁ מִצְרִי, מִיַּד הַיִּשְׁמְעֵאלִים, אֲשֶׁר הוֹרִדֻהוּ שָׁמָּה. 1 And Joseph was brought down to Egypt; and Potiphar, an officer of Pharaoh's, the captain of the guard, an Egyptian, bought him of the hand of the Ishmaelites, that had brought him down thither.

From: http://www.mechon-mamre.org/p/pt/pt0139.htm

Answer 1

If you simply read the "pshat" as recorded, it seems to work quite nicely (partly taken from Rav Menachem Leibtag).

The brothers see Yishmaelim and therefore decide to sell Yosef.

Before they get to it, Midyanim come and take him out of the bor (i.e. the pit) and sell him to the Yishmaelim (to bring to Egypt).

Since the Midyanim, in effect, did the selling (to Egypt), they are said to have done as such.

But, who actually handed him over to the house of Potifar? The Yishmaelim did.

Answer 2

Yosef's brothers pulled him up from the ditch and sold him to the Yishme'elim who sold him to the Midyanim who sold him to the Medanim who sold him to Potiphar (Sifte'i Hakhamim).

To answer the second question: no (see above).