zebra finches - babies

Question
I have two pair of zebra finches.  One pair has no problem having babies and the other pair has problems.  They sit on their eggs continuously but they do not hatch.  The other two are not so loyal to the eggs and yet they keep having the babies.  After the babies are a certain age however the male bird starts attacking them to make them leave before they are ready.  The last cluth they had about three babies one died young and the other two were having problems getting the care they still needed.  We tried to feed them ourselves but one died almost right away leaving only one.  After a certain age (not really old enough) the male pushes them out of the nest and then pecks at their head until they are bald and continues this until they die (their first clutch).  So this time we removed the male from the cage in order to save the last of this second cluth from dying and it worked.  Her feathers grew back within 2 weeks and the female continued to care for her on her own and all was well.  They now have a new batch of babies about 4 I think. The other pair of birds are still trying to hatch eggs that must not be fertile.  Is it possible to try to put a couple of the babies from the parent birds nest to the nest that can not hatch babies for help with the care of these new babies before the male starts killing them off?  This is the 3rd batch of babies within a year for these very fertile birds.  Do you think the other two birds will be good foster parents if we try that?

Answer
Since they sit so faithfully on their eggs, I think they will be. The best way to go about this is to give the eggs from the fertile pair to the non fertile pair. If you give them babies they may try to kill them. So make sure they're eggs. The best time is when the female also has eggs but zebras have a hard time remembering which eggs are theirs and which ones aren't.