The story of רות and conversion

The story of רות poses many problems for orthodox Judaism especially with regards to conversion.

When did רות and ערפה convert? There are 2 possibilities:

1. They converted before they married Machlon and Kilyon
2. רות only converted with Naomi much later

Both possibilities appear in Chazal and both are very difficult. The Medrash Raba states that they did not convert before marriage and this is the opinion that Rashi (on the Megilla) adopts. On the other hand the Zohar states explicitly that they converted before marriage and this is implied in the Gemara in Bava Basra as well which states that Machlon and Kilyon were punished for leaving Israel in a famine leaving out the much bigger sin of marrying non-Jewish women.

Issues with conversion before marriage 

1. The Gemara learns out many dinim of גירות from the conversation between Naomi and רות, yet if they converted before marraige why was an additional conversion needed?

2. If ערפה converted before marriage how could Naomi tell her to go home to her people and Gods, she was a Jew, a convert?

3. Naomi tells רות that she doesn't have another son implying that if she did רות could marry him, yet this situation is actually prohibited by halacha (see Rashi there)

Issues with a later conversion 

1. The Gemara calls Machlon and Kilyon Gedolei Hador, how could the Gedolei Hador marry non-Jewish women?

2. How exactly did Naomi convert רות, she is not a Beis Din and cannot convert anyone

3. It sounds like Boaz was מייבם her, yet if she was not Jewish when she married then there can be no Yibum as the marriage was no marriage and her subsequent conversion wipes out any family relationships that she had.

Conclusions

There is a clear contradiction in Chazal as to whether רות was מגייר before marriage or much later. Both options have very serious questions as listed above and would seem to indicate that conversion was a very different process then.