Is Survival of a Startup possible on Freelancing through websites?

We are a team of four (and great friends) and have a good product in mind and initial RnD shows great potential (Server based application).
But the problem is that we need to spend around 1 and a half year to develop it. Funding is naturally important so we thought of freelancing to keep ourselves well off.

If we keep ourselves to Websites such as ODesk or freelancer or elance, can we create ourselves a decent earning ? and we specialize in Desktop Applications.

If not or if yes please advise us as well.

Your mileage will vary. You will be competing with very low cost labor from developing countries, including heavy hitters from the Ukraine with very impressive portfolios.

Programmers and designers on those sites are a dime a dozen.

You are also starting on there with no Odesk reputation (many of the offshore consultants have agencies with many ratings).

You can try applying to some jobs there and see where it goes, probably having a very extensive portfolio and lower prices will help. People who go to those outsourcing sites have a very low cost mindset, of course there are exceptions.

Now, that being said, if you can create an agency and leverage the work of others - you may have some chance of making good money there.