How can I order rows returned by the RETURNING clause of a DML statement?
You need to apply an ORDER BY to the result. To do that, put the DELETE statement into a common table expression. Then you can apply an ORDER BY when you select from it

with deleted as (
  DELETE FROM @tableName
  WHERE id = ANY (
        SELECT id
        FROM @tableName
        WHERE source = :p1 AND target = :p2 @readCondition
        ORDER BY createddate
        LIMIT @limit
        FOR UPDATE SKIP LOCKED)
  RETURNING *
)
select *
from deleted 
order by createddate;