It's always worth trying to sell rather than letting them expire. Your how to domain isn't bad for a minisite though I don't see it getting a ton of traffic. You should at least try parking them as well - then you can gauge if they get any traffic/revenue - that can improve your chances of selling them.
those keywords inside those domains you've mentioned try searching them on google.com the first 10 or 20 search results you have contact them either via form or email or both