My first choice for Forms 2 and 3 is Lively Latin. Start with Book 1, then move on to Book 2. Both books should last 2+ years each. It comes with an audio option and an online option. And it’s fun!

Another option for Form 2 Latin is Minimus. 

Book 1 Teacher’s Guide

Book 1 Audio CD

Book 1 Student Workbook

Book 2 Teacher’s Guide

Book 2 Audio CD

Book 2 Student Workbook

Also available at Rainbow Resource here