I am also trying to rehome 4 ducks! They are all 7 weeks old. 2 are welsh harlequin (males I think) and the other two are welsh harlequin x blue Swedish mixes. they are very pretty but I sadly don't have enough space for them. If you would like them PM me.
Do you have a thermometer under the heat lamp? Are all the chicks crowding under it or on the other side of the box? Have they drank and water and/or ate any food?