Use Same Pin on Multiple Different Shields

Projects General Guidance
1

Is this possible?

2

Some pins are designed for multiple use, like the SPI interface or the I2C/TWI interface. In most other cases you can't use the same pin for two different shields. Sometimes you have to use a breakout board instead of a shield so you have control over what pins the device uses.

3

michael-:
Is this possible?

Sure, often called "common ground".