I think we're finally going to apply for citizenship. One initial question I have, though, is whether I need to file applications for my daughters ages 16 and 18, or will they automatically become citizens when my husband and I do? -?
I think your 18 year old will have to apply in her own right. Your 16-year old will only get derivative citizenship if you and hubby both become American citizens. I think the form for her is N-600.
Also I think the 16 year old would have to confirm her wish to be a US citizen when she turns 18. Given the time it takes to go through the process and the fees involved, and depending on exactly how old she is, she might want to consider waiting to make her own application. (i.e. if she is close to her 17th birthday, she might have to go through the process again in a year).
Certainly something to look into.