please not that a given task can be performed only by a single actor. Of course it can be assigner to many users/groups but in the end only single one can claim and work on it.
What I would suggest is to create multi instance of that task that will get list of users that need to vote as input which in turn will create task for each of them. At the end you can collect all votes and do whatever is needed with it. Multi instance will guarantee that it will finish only if all tasks are completed.
HTH