The loss of a child is said to be one of the worst things that can happen to a person/couple. Especially, since you have not gotten to experience the joys just heartache. I hope things work out so you can experience the smiles, giggles, and love a little person can bring. This religion almost acts like children are a burden and disadvantage in serving God, its sick.
I don't have experience with stepping down... and we were fading before we were even awake due to circumstance. I do believe because of your wifes grief, the shallow sympathy, and complete lack of understand with your losses, you may be able to win her over about how shallow-empty this religion is.
Being a women and a mother, I don't know if I would go and tell her you don't believe right off, only you know her, but... she has serious emotions due to grief, I don't know about adding the grief of a husband who fell away.