Adding more bees and brood will help boost the population before winter. Go for it.
Any foragers on those frames will return to the old hive leaving behind the nurse and house bees. Just don't overtax the donor hive.
If there is a dearth,be sure to have adequate feed for the new hive so the queen keeps laying. It would be counterproductive adding brood while a queen is layed back on laying because of a dearth.