multiple user want to act on single task before completion

Hi

I have a requirement in BPM process where every task need to be processed by multiple users .Each user will see his corresponding data to validate in task UI .I have assigned multiple potential user to the task .They are getting the task in there worklist once the process is initiates.

But the issue is if one f the potential user claims and act on the task .the task goes of from other user's list but it remains incomplete as others have not acted on it.

How can I achieve this.

Thanks in Advance

Poonam