Suggestions for Designing a Process Model

@praveenkumark,
1st scenario,you can handle in 2 ways:
1) If data is same for all the instances then under the MNI section of user input task you need to select "Automatically run multiple instances of this node" and
specify the PV variable in "Run one instance for each item ". This overrides all the previous instances(considers the latest 50th instance by overriding other 49 instances).
2) If each instance data is required you can select : "Run one instance for each assignee". This stores each instance.

In the 2nd case: Add all the 50 members to a group and add that group to the assignment,this restricts single user at a time,if 1 user accepts the task others would not be able to see the task.
Please let me know if this is not the case which you asked for...

@praveenkumark,
1st scenario,you can handle in 2 ways:
1) If data is same for all the instances then under the MNI section of user input task you need to select "Automatically run multiple instances of this node" and
specify the PV variable in "Run one instance for each item ". This overrides all the previous instances(considers the latest 50th instance by overriding other 49 instances).
2) If each instance data is required you can select : "Run one instance for each assignee". This stores each instance.

In the 2nd case: Add all the 50 members to a group and add that group to the assignment,this restricts single user at a time,if 1 user accepts the task others would not be able to see the task.
Please let me know if this is not the case which you asked for...