I would suggest that they both take the SAT or the ACT if it's convient. I would also consider giving them the same Iowa test they currently use, but up a few grade levels, so you can see what they "don't know." It's a good idea to know where they stand in relation to other kids so that as you look at Online, correspondence or University courses you have an idea of where to start them.
As they take classes the correspond to SAT II or AP classes, you will want to be able to document their work with those subject standardised tests as well.
Are you in the USA now? Returning to Thailand soon? Will you continue homeschooling? Are you doing all of the teaching or have they started to suppliment with outside resources?
Smiles,
Trinity
