Booking onsen for 12/28 to 1/3

Hi there,
I want to book onsen hotel for 12/29 in Kurokawa and Beppu on 12/30.

1) Any recommendation for those 2 areas? There will be 4 of us (my wife and I and 2 kids) and my wife prefers one that offers a private bath.

2) How can I book them? I had been using Japan Guest Houses for previous Onsen bookings, but looks like they don't support booking at this time period because they will be close.

3) Another question that I have is if we fly back to Tokyo on 12/31, will the limosine bus/airport still operate in normal hours? We notice most shops were closed on the 31st after 5pm when we were there 2 years ago, so figure using 31st would be a good day to fly back as we would lose half a day anyway, unless the airport/limobus are not available.

How can I book them? I had been using Japan Guest Houses for previous Onsen bookings, but looks like they don't support booking at this time period because they will be close.

Who are "they"? Japan Guest houses? Or Ryokan in Kurokawa and Beppu? Note that you will hit the most busy touristic dates in Japan in one of the most popular onsen places in Kyushu. Of course most if not all ryokan will open these days since these are the busiest dates. I checked via Rakuten and Booking.com and found not so many ryokan have vacant rooms (and they are rather expensive). You can search some booking sites and if there are suitable ones, just book it. Or you might better contact with some travel agency such as JTB and tell them your preferences. You might have to pay some handling fee, but it will not be so expensive (the handling fee I mean. The room rate should be very expensive if you like private open air bath).

will the limosine bus/airport still operate in normal hours?

I forgot to answer. Yes.

I personally like jalan.net for booking hotels and ryokans in Japan, but as PP said a travel agency might be a good option too. And yes, these dates are VERY popular. Book as soon as you can.

At least in Kurokawa going for a ryokan with private bath is loosing out on the great onsen experience you can have there. There are so many extremely nice onsen, you should really convince your wife to have a dip in the shared ones. They are gender segregated anyway (I think a few when we were there were not gender segregated, but most of them are, and you can get the information at your ryokan easily). The best of them is without doubt Yama-Mizu-Ki.

Enjoy your trip to Kyushu!

I tend to either go direct to the ryokan's website and book from there, or go via booking.com, japanican, or the other usual booking engine suspects.

The ryokan's website is best if you want to book a particular room, or for booking a particular dining package (if you look on the ryokan's website, you very often see that they will offer a range of meal types, at different prices. Booking engines typically don't have that level of detail as an option).

I would also definitely recommend staying in a different ryokan each night, for variety of food and bathing. In Kurokawa, definitely go and get the onsen pass and spend a few hours walking from inn to inn, sampling the different baths. One or two of them have mixed bathing...