Who owns the code under Dual Licensing - GPL/Commercial License?

Question

Licenses for software and other works

I am developing a dual licensed project. The GPL is chosen as a free license, but a commercial license is also assumed. The bottom line is that the source code is developed and published on Github. I am ready to accept the contribution of third-party developers, but what about the rights to a commercial license in this case!? After all, even though, let's say, most of the code will be mine, there will still be contributions from other developers in the codebase, and, in this case, how does this compare with a commercial license and dual licensing? Perhaps this should somehow be prescribed in the commercial license itself?