I find formatting can help. List each of your questions at the bottom of your emails, so they can go through them and answer them one by one. It's also harder for them to justify answering one question and ignoring the rest when you lay it out for them in one place.
Depending on the questions and how much the answers matter, it may be better to ask each one after they reply to the previous one, so they don't feel overwhelmed being asked all of it at once and put more thought into answering each one.