Can we get a visa for china whilst in Katmandu, Double entry?? If so how long does this visa take?

It is possible for you to get a China tourist visa in Katmandu. But I cannot guarantee. And even if you can get one, there is a great chance it will be a single-entry one. Anyway,you my give it a try. State the reason why you need a double-entry visa while applying for the visa.