The basic thing here is that "would" is the past/conditional of "will".
Q1:
"Share" is an action, not a state.
Consider this present/future situation:
Mother to daughters, "When we visit your grandparents, you will share a bedroom."
Daughter telling her daughters about her childhood, ""When we visited our grandparents, we would share a bedroom."
If you don �t eat breakfast, you will get hungry before lunchtime.
I remember that on days I didn �t eat breakfast, I would get hungry before lunchtime.
q2
"Would" needs a situation.
I wasn �t worried because I knew she woul have four pairs of sunglasses in her purse.
Q3
Again we need a situation.
Leo won �t use his cell phone if he can use e-mail.
Leo wouldn �t use his cell phone if he Could use e-mail.
Bruce