When you assign a task in workflow the permissions for the task happen automatically. If you assign to a person, only that person can respond (or it can be delegated by site owner). If assigned to a group, only members from that group can respond.
Thanks for your reply.
Yeah I understand this scenario, But my requirement is in the same group only other members should not be able to edit the same form if one user is already working on it like if user has marked the status as "In progress".
Awaiting for your reply.
Thanks and Regards,