Hello Stefania,
Currently, it is not possible to create 2 patches for the same solution in the SDK.
However, i don't know your real process for your dev. why don't you do the fixing and another phase in the one patch?
If you want seperated manage the dev, you can create another new solution. however, you cannot refer the objects from another solution, unless you created external web service, but this is more effort to manage the lifecycle.
Regards,
Qiang