Currently, OOTB review tasks are sent to all the reviewers in parallel (all reviewers get the task at the same time). Can users dynamically decide during the WF execution some tasks users to get parallel tasks some to get sequential tasks. Every time the workflow is executed, the task could be either parallel or sequential or both. And the number of reviewers varies each time. Is this possible in Tc workflows?
your need seems is very specific. May be you should build your own handler to set your reviewers as described.