kbmMemTable contains several methods for copying from other TDatasets.
One is CopyRecords.
Or if you yourself has an editable/appended/inserted record spot available on the destination, you can use AssignRecord(sourceds, destds);
Both will automatically figure out which fields to copy. CopyRecords will even allow you to map fields to other field names if needed.
Fields in source table fld1a and fld2a is mapped to destination table fields fld1b and fld2b.