Kepner Cobi Project Lead/Sr Engineer

We are looking to setup a parallel task that can be assigned to two specific users from a list. These two users will be selected from a group in order to be assigned to the parallel task. The assigned users will change, so it won't be possible to create a group for each option. How can we set up this process to allow the users to be selected and assigned to the parallel task in a dynamic manner from a workflow task?