If someone has an older child, can they start AAS at level 2?

NO.

Everyone must begin All About Spelling at level 1 no matter what their age or background. AAS teaches spelling using the Orton-Gillingham process. It is more than just a spelling program; it is an entire process. The parent is learning how to teach it right along with the student learning to use it. If you start in level 2, you have missed important foundational steps that seem simple, but are critical.

Yes, you may breeze thru level 1 in a month or two, but it is worth it. It is a very popular program, so it will sell used in a heartbeat.

You only need one Basic Interactive Kit to teach ALL your kids, and you MUST have it--can't teach the program without it.

You need the student materials (that is why it comes with the Teacher's manual--can't buy a teacher's manual without a student pack!), but you can get away with one pack per family. You can initial cards when one student masters it, or just keep using the cards for both till they both master it. Of course, if money is no issue, buy a second set!