Confussion in deciding this twins birthday

SOMEONE SHOULD PLEASE HELP ME OUT.
If a pregnant woman gives birth to two babies; the first one comes out at 11:54 PM of December 31st 2016, the second at 12:03 AM of January 1st 2017.

QUESTIONS    
1. Are they twins?
2. Are they age mates?  
3. Which year will they claim?
4. In which year will they celebrate their birthday?


THANK YOU.          😀😀😀