Sure you can, but you need to go out of US to change back to H-1B after your H-1B approval.
2) my wife is on her H1b. If she switches to EAD, can she continue her H1b in case my I485 gets denied (without applying a new H1b for same empployer)
If she switches to EAD, she will be in the same boat as you, as after using EAD, her H-1b will be void.