Legal contract for authors rights

I have a media company (registered in England and Wales) and I hire authors to write stories, novels, dictionaries etc.
I want a generic legal document - contract to cover my company with:
a) an authors declaration that the content is original and not product of copy/plagiarism and if it is, only the author is responsible
b) an authors declaration that he grants (or sell or transfer) all the rights to my company to publish the content in any language and international. In simple words I want something like the authors write the story on behalf of the company and the company has the rights for everything. The author with this contract has no claims from the company and he cannot resell it or publish it in different languages or countries.

You can ask higher or lower price.
Thanks