Are James and albus potter twins?

Answer 1

No. They are distant cousins. All pure-bloods are related in some way, James Potter was the last pure-blood from the Potter line and Voldemort's mother was the last pure-blood in the Gaunt line.

Answer 2

Not directly but since both of them has pure-blood relatives they are related in some small way. Albus Dumbledore was Lord Voldemort's headmaster and later his enemy.

Answer 3

No James is a year older than albus he was going into his second year when albus was going into his first.