In the Mahabharata, Adi Parva, Chapter 105 when Satyavati coaxes her son Vyasadeva to give her grandchildren, he say this:
'If the princess of Kosala can bear my strong odour, my ugly and grim visage, my attire and body, she shall then conceive an excellent child.'
'Let the princess of Kosala clad in clean attire and checked with ornaments wait for me in her bed-chamber.'
Satyavati then went to her daughter-in-law and seeing her in private spoke to her these words of beneficial and virtuous import, 'O princess of Kosala, listen to what I say.'
So, what do they mean by this? Weren't Ambika and Ambalika the daughters of the king of Kashi?