Did the eggs turn bad or did they come out of the females already bad?
You can't rule out that some males can have bad sperm.... Were the 2 bad clutches fathered by the same male?
How did you try to incubate them? Could've got too moist, too hot, too dry, etc..

I'm not sure about house snakes and brumation but I'd assume they go through a cooling cycle like other colubrids before breeding.

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Mike
KingPin Reptiles
www.kingpinreptiles.com