All users need to work while linked to the same central catalog and all designs should be based on the same template (should be linked to the central catalog as well) it is advised that template will be locked with password (to eliminate any unintentional changes in any of the designs) .
The leader should export the BID design and the others 3 guys which work on WID should import it . so any of them will generate the WID base on the BID. at this point any of the guys which work on the WID can check his portion of WID against the BID.
If any change is required to the BID sheets - it should be done by the leader - and sheets should be exported and imported again
if any change is required to design properties (i.e. additional parameter) - this should be done by the leader on the template design and changes should be propagate to all designs by exporting design properties.
The WID guys should export their completed sheets and the leader should import all to his single design ; it should generate complete BID/WID design.
This is iterative process - export/import can be done multiple times according to progress