Hi sorry dont know anything about breeding finches.I had a pair years ago they laid an egg twice but despite sitting on it it never hatched.They lived together for 10 years indoors,one got stuck behind the cooker,the other found its way into the cats mouth twice but they still lived on then one day the female died 1 hour later the male died.I buried them together under a apple tree in the garden.Good luck with your dilemma im sure someone here can help.