Lovelines (aka The Eddie) - S6-E19
Character mistake: In the scene when Dr. Drew has Joey and Eddie on stage, they are arguing and Joey says that Eddie moved away and dumped her twice. Actually, he only dumped her once, when he moved out of his apartment and back home with his parents. The 2nd time that Joey is referring to is when Eddie moved to California for the writing workshop, which SHE helped and encouraged him to do. So he did not dump her 2 times; she basically pushed for him to leave the 2nd time, yet she acts as though this situation never occurred.
Answer: They are not twins (Jack is older than Andie). It is possible due to when birthdays fall in the school calender for non-twin siblings to end up in the same grade. Say that you have to be 5 on Sept 1 to start Kindergarten, you are born on Sept 2, 2000 and your little sister on Aug 30, 2001. Sept 1, 2005, you are 4 years and 364 days and can't start. So Sept 1, 2006, you are 5 years and 364 days and your sister is 5 years and 1 day, and, voila!, you're both in the same grade.