If you ask in an absolute sense then of course there is no such free will operating independent of everything else. Always we are pushed by forces. Yet something is apparently at least given in our hands. It is the choice of attitudes we take towards circumstances. That is the difference between Arjun and Karn. Both have a difficult childhood. But one becomes an instrument of the Divine, the other stands by the side of the Asura. Of course there are lives behind this choice that sealed their respective destinies. Behind it all there is of course a pressure of the Divine seeking to manifest through the tangle of circumstances. However since most human beings as well as gods do not respond to the Divine Will in a straightforward way, therefore the distortion gets introduced in creation and it takes such a dramatic often disastrous route towards the fulfilment of the Truth concealed within creation. That is one of the lessons of the Ramayana and the Mahabharata. Was the destruction necessary. The answer is yes and no. If those involved responded to the Divine Will it was completely avoidable. But since they did not it became inevitable.
Affectionately,
Alok Da