Need help for Parent's Visa approval

Hi all,
I am currently in London and I had applied for Entry clearance for my parents for UK,but they rejected it specifying that they are not happy about my father's leaves approval. I was wondering that if I will sponsor all their journey/expanses, for that I will send my documents but still does he need to submit some documents assuming he is a government officer.
He had submitted his property papers, his bank stmts and incom tax return for three years. what else they require. Could anyone suggest me plz.
Thanks very much.