Core Pega - 8.4.4

Pega CFW (AKA Windows Mobile Client) - 8.40.10

Our use case is while the users are offline and in CFW, users will have Inventory master data WO as the Parent. When the user creates a child maintenance case we would like the Inventory data  from the Parent WO to be copied to the child initially. Once the child maintenance WO is resolved, we would like to update the child inventory data back to the Inventory master data Parent WO.

For Ex: Initially if the parent has 10 trucks, copy all the data to the maintenance child case i.e. 10. Now, child case consumed two trucks then we would like to update the parent with 8 trucks. The future child cases will have 8 trucks to work with.  

Can someone suggest how to accomplish this as we are facing challenges updating Parent WO while working with Child?