Hi RanjeethRao -
Using a dSource, when you spin off a VDB in archivelog, you should be able to use Flashback Transaction Query making sure appropriate UNDO* (UNDO_MANAGEMENT, UNDO_TABLESPACE & UNDO_RETENTION) parameters are set right on that VDB.
VDB Snapshot Policy itself will take care of maintaining appropriate retentions of both Snapshots and Archivelogs of the VDB's. You don't have separate VDB retention policy.
Hope this helps.
thanks
Ganesh