It is said that Nara-Narayana sages were born as Arjuna and Krishna respectively. But at the same time Arjuna is biological son of Indra.

Also it is said that Draupadi is incarnation of wives of Dharma, Vayu,Indra and Aswini Kumaras. 

So my questions now are

 - Whose soul did Arjuna have? Indra's or Nara's ?

 - If Arjuna had Nara's soul (Atma), is this the reason why Krishna exhorted Bhagavadgita to Arjuna, indirectly saying to himself ?( Lord Vishnu was born as Nara and Narayana brothers.).
 - If assumption in second question is correct, is this the reason behind their friendship?