Who did the שבטים marry?

The past few parshas have focused on the 12 שבטים, the sons of Yaakov. As opposed to their father and grandfather, where the Torah had a long story about who they married, the Torah is basically silent about who they married. Rashi, quoting Chazal, offers 2 conflicting opinions on who they married both quite problematic.

1. They married כנעניות
2. Each שבט was born with a twin sister whom they married 

Marriage with כנעניות

There are a number of problems with this approach:

1. Both Avraham and Yitzchak went to great lengths to ensure that their chosen son didn't marry כנעניות and sent them off to find wives. Therefore it would be very strange for Yaakov to allow his sons to freely marry כנעניות who were cursed.
2. What exactly was the status of these כנעניות women? Did they convert? If so, how exactly? Remember, that in Judaism who is a Jew depends on the mother not the father. 
3. After Yosef is assumed to be dead the Torah states וַיָּקֻמוּ כָל בָּנָיו וְכָל בְּנֹתָיו לְנַחֲמוֹ. Who exactly were these daughters? Additionally, the Torah says בָּנָיו וּבְנֵי בָנָיו אִתּוֹ בְּנֹתָיו וּבְנוֹת בָּנָיו... הֵבִיא אִתּוֹ מִצְרָיְמָה, again who were these daughters who went down to Egypt?

The twin option

Rashi comments (based on the medrash) by the birth of Binyamin that a twin girl was born with every שבט and that is who they married. רבי יהודה אומר: אחיות תאומות נולדו עם כל שבט ושבט ונשאום. However, this raises a number of questions:

1. How could they marry their twin sister, even if they weren't considered Jewish, בני נח are also prohibited from marrying their full sister. The Ramban explains that they didn't marry their twin rather they married a sister from another mother so as not to violate the issur of incest.  However, the simple reading of the medrash is that each brother married his twin sister which is prohibited even to בני נח as one of the עריות.
2. Since the wives/daughters were Yaakov's children how come they are not mentioned in the count of 70 going to Egypt. Rashi comments that you have to say that they all died before that, however, that is clearly very difficult.
3. The Torah states explicitly that Yehuda married שוע a כנענית. Rashi explains that you have to say כנעני means a merchant. The same would have to go for Tamar as well. Even with this interpretation, Yehuda didn't marry a twin but rather an outsider. If so what happened to the extra twin? Who did she marry? 
4. In ויגש when the Torah lists off all the descendents of Yaakov, Shimon has a son שאול בן הכנענית. The simple understanding is that Shimon married a כנענית. Rashi explains that this was really Dina (this raises a different issue to be discussed later). THis raises teh same question as with Yehuda, if Shimon married Dina then that left another twin daughter with no one to marry.

Who did Dina marry?

After Dina's rape by Shechem we hear nothing about her until she is counted as one of the 70 going down to Egypt. Rashi quotes 1 opinion that Dina married Shimon and their son was שאול בן הכנענית. However this is very problematic. Dina and Shimon were full siblings (same mother and father). Therefore, how could they marry? Even a Ben Noach is not allowed to marry his full sister. Another opinion in Chazal is that Dina married איוב. 

Conclusion

As usual, we find that there is a dispute in Chazal about who the שבטים married with 2 contradictory opinions. Additionally, each opinion has it's share of difficulties fitting in with both the text and what we know and again the questions seem to better then the answers.