I was surprised to hear that they ask candidates to spend a couple of days working on a project, and then present that project to the company. That's a substantial time investment to ask someone to make on top of interviewing. If I was looking for work and every potential employer asked this of me, searching for a job could take weeks or months.
Maybe give them a project that only takes a couple of hours, just creating a simple module that does some very basic thing. Try to find out how they work rather than the final result.