transactions - Who sells Yosef? Who brings him to Egypt?

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