No, that's not possible right now. It's unlikely though that we will be adding this feature. For tasks that needs to be assigned to multiple people, it's best you break them down to sub-tasks.
We've published a post explaining why it's best to have one specific individual responsible for a task. You can read it here: https://todoist.com/blog/2014/05/using-steve-jobs-strategy-to-assign-tasks-in-todoist/.