Actually, all of my best suggestions for those things are in the article above. One challenge you’ll have is that all popular tropical destinations have their peak weeks at the end of December because so many people in cold areas have that time off. So flights to Central or South America are going to be fairly expensive, although buying soon can help. For hiking and views I think Costa Rica could be a good choice, or Nicaragua. You could also go to Bariloche in Argentina, though it’s probably not worth going all that way unless you were also going to spend some time in Buenos Aires and such.
However, I would probably recommend staying closer to the US, unless you are really interested in the Asian cultures or that kind of experience. If you are mainly just interested in family time and a fairly easy holiday for all, and you aren’t specifically interested in getting to know an Asian culture and its food, I think I’d stay in the Americas.
As with most on this list, hotels get very full and more expensive just before the Christmas holidays, so it's better to come early in the month if possible. That way you'll have your pick of places at some surprisingly good room rates, even at some high-end places on the famous beaches. If you are coming during Christmas then book a hotel NOW because they'll be full and will keep getting more expensive the longer you wait.
Southeast Asia is easier to deal with, and there are cheap flights connecting in the Middle East and landing in Bangkok, Kuala Lumpur, and Singapore. Each of those is a very interesting city, and there are many smaller places to go in the same region. In Malaysia there is Penang and Melaka. In Thailand there is Chiang Mai and quite a few others in that area. In Laos you can visit Luang Prabang, which sounds like it could be a winner for you. And there is also Siem Reap, which is home to the amazing Angkor Wat temple complex.