Answer:
1. Yes, the two babies are twins.
2. It depends on the country's legal definition of "year of birth." Some countries consider a person to be born in the year that they are delivered, while others consider a person to be born in the year that they are conceived. If the country considers the year of birth to be the year of delivery, then the first baby would be considered to be born in 2018 and the second baby would be considered to be born in 2019. If the country considers the year of birth to be the year of conception, then both babies would be considered to be born in 2018.
3. Both babies will celebrate their birthday in the month of January.