I have to say I'm not sure. Zebra finches can breed year round in captivity. You can try removing them again, try rearranging the cage at the same time. Best outcome is they stop laying for awhile, worst outcome they start laying somewhere again. You know your birds better than us, and your little ones have been very determined. If I were in your shoes I may try removing the nests again, but I would also remove any and everything nest like in a hope to curb laying. I would continue to offer water soluble calcium grit.
Zebra finches are from the hostile and difficult climate of the Australian Outback. In the wild they lay based in the environmental conditions, as soon as there is enough food and water. This is why it is harder to regulate zebras in captivity, because in the paradise of our homes there is plenty of food and water all the time. It will always be a balancing act because we will always take the best of care of our little ones.