I am about to file 2008 tax return when I remembered my parents-in-law lived with us for 4 months in 2008 (Apr to Aug) under tourist B2 visa. They didn't have any US income. It is required that I fill in SSN or ITIN to claim them as dependent. I have the following questions:

1) Do they have to be 65 or older to be claimed as dependent?
2) Is it too late to apply ITIN for them? (they are no longer in US)
3) How to apply ITIN?
4) Will I be able to get ITIN in time to file 2008 tax return?
5) If I don't get ITIN in time, can I not file them as dependent for 2008 and make correction in 2009 tax return?

Some additional info:
- I am filing jointly married with my husband, we are both permanent residents.
- I am holding Taiwan passport, my husband holding China passport
- my parent-in-law are China citizen holding China passport visited US with B2 tourist visa

Any answer/suggestion/advice is appreciated!

Thank you.

You cannot your parents as dependents, as they have not met the Substantial Presence Test to be considered residents of the U.S.