Set up the brooder with a piece of scrap hardware cloth if you have it wrap edges to cover the sharp edges place one on each side and see how that goes. Try them together it may work but if it doesn’t you’ll be prepared. Probably won’t take long for the older to accept the younger. They thrive...
@BlueO you should get a thermometer and check the temps. there should be a cool side in the brooder so they can get out of the heat. I'd go with a larger tote. And that feeder is for chicks ducklings have a wider bill as they grow they will have a hard time drinking out of that feeder they need...