Fun! 🙂 With some birds, letting them sit on the eggs until they get tired of them can work and help break the egg laying cycle. You could leave the egg for now, as long as the other bird can get food from another cup. Then when you get the smaller cups, besides changing to those, you can try some other changes to discourage egg laying. Try limiting their light to 8-10 hours per day by covering the cage early each evening. You can also try moving the cage weekly to another spot in the room, and make sure it is in a place where it is busy – not a quiet corner. You are already doing the right thing by not having nests. And maybe adding toys can also break up the nesting mode.
Thanks for the update,