Last minute family trip to Hokkaido

Hello, just found some vacation time and was hoping for some help planning a last-minute family trip to Hokkaido. Today is Thursday and I am thinking about going there in two days, Saturday. I've checked and can book flights into either Sapporo (Chitose) or Memanbetsu. I really want to go to Shiretoko as it looks beautiful, but it is out of the way. We would go for 6-7 days. I would be traveling with my wife and two kids (both under 8).

Apologies for some of these basic questions but I am running out of time to research everything before my trip.

First, before I confirm my flights, is it realistic to be able to book the car rental and hotels on such short notice? I usually plan ahead so am a bit nervous about booking everything on short notice without properly reading reviews etc.

Second, is Shiretoko worth visiting on a 6-day trip? We like hiking and nature; less concerned about food although I need to be able to feed the kids (rice is fine).

Third, are there any particular family friendly hotels/guesthouses between Shiretoko and Sapporo that will allow my entire family in one room? Is this fairly common?

Fourth, does it make sense to travel from Memanbetsu to Chitose on a 6-day trip? Is it worth spending one entire day traveling across Hokkaido? I've driven across the United States and Australia so don't mind a long drive as long as it is scenic and there are places to stop and sightsee.

Fifth, what are the key family friendly highlights (other than the national parks) between these two points?

Finally, if we go, which car rental agencies are best to rent from (if arriving at Memanbetsu)? Are there usually cars available on arrival at the train stations or airport?

Thanks in advance, and apologies again for these basic questions. Appreciate any answers you can spare.

For car rental, you can try using this link:
http://www2.tocoo.jp/?file=rentcar_inbound/main
I find the rates they quoted me is better from the others. But you have to act fast because their business days are from Mon-Fri till 4pm. Also, due to summer holidays starting from end of July, certain car class/model might not be available. Same goes for the accommodation as well.

For car rental you can't go wrong with Toyota, just that their rental rate is generally higher than others. ToCoo is a popular budget rental agency with many connections. Both Toyota and ToCoo have outlets in Memambetsu Airport, but do note that if you pick up in Memambetsu and return in Sapporo or Chitose there will be an additional drop-off charge for the rental car.
http://rent.toyota.co.jp/rental/1-4-1-2.asp?sFlg=1&sCount=&rCode=61601... (Toyota)
http://www2.tocoo.jp/?file=rentcar_inbound/branch_list_all2_area&listn... (ToCoo)

Booking the rental car and accommodation beforehand is recommended as Hokkaido is very popular during summer months. Do not be surprise if lodging in places like Furano, Biei and Shiretoko Peninsula are hard to find at this late date.

Shiretoko Peninsula is indeed a paradise if you are into nature and the great outdoor. We spent 2 full days there and wish we could stay longer. Between Shiretoko and Sapporo there are lots of interesting places worth visiting. The concern is whether you can do all in just a few days! I will leave it at that unless you really decide to pursuit this route and then I would elaborate a bit more.

With not enough time for detail planning I would recommend a simpler plan which I think is more suitable for a short 6-day trip. Fly in and out of New Chitose and spend 2 days in Sapporo doing a day trip excursion to Otaru using public transports. Then with 4 days pick up a rental car to do a loop drive up to Asahikawa taking in Furano and Biei, hopefully staying a couple of nights in between. The drive will be much shorter, more relaxed and there would not be any steep drop-off charge. July is the best time for the lovely lavender and rainbow colour flower fields in Furano and Biei. You kids can go for some farm visits with close encounter with cute animals and also some hands-on experience in dairy products. In Asahikawa you can try out the best ramen in Hokkaido and again kids can enjoy the popular Asahiyawa Zoo. In Otaru children will love the DIY experience of music box and glassware souvenir.

Another merit is by renting a car in Sapporo you get the best of both world because you can get hold of a Toyota through ToCoo.
http://www2.tocoo.jp/?file=rentcar_inbound/branch_list_all2_area&listn...
Or if you still want a more competitive rate, try Kakuyasu. The only slight inconvenience is that you have to pay beforehand rather than upon arrival.
http://shiretoko-t.com/en/

Thanks all for the replies.

I still want to do this trip tomorrow, so have a lot to plan between now and then.

Here is the outline for our trip. Would appreciate any advice on whether this is feasible or if I am missing any key highlights. Only thing I know is that Shiretoko, the zoo, and the lavender fields are musts, along with good seafood at Kushiro. Anything else would be a bonus.

Still have no idea on where I am staying, so would appreciate any recommendations on hotels that are family friendly (2 young kids). Normally, I am very good at planning but I only found out I had time to take a trip 36 hours ago.

I have found a car at timescar-rental.com. The one-way drop off fee is 7000 yen which is fine. Are they reliable?

For hotels, any recommendations on which booking engines I should use. My key concern is getting my first two nights in Sapporo confirmed first, and maybe my third night in Asahikawa.

THANKS AGAIN!!!

Sat / Day 1
Fly to Chitose, transfer to Sapporo
Night in Sapporo

Sun / 2
Sightsee
Night in Sapporo

Mon / 3
Pick up rental car
Drive to Asahikawa for the zoo (for the kids)
Visit Daisetsuzan National Park time permitting
Night in Asahikawa

Tues / 4
Drive to see flowers around Furano
Evening drive to Kushiro
Night in Kushiro

Wed / 5
Travel around Kushiro area (Lake Akan)
Night in Kushiro (unless there is another town between Kushiro and Shiretoko that we can stay overnight at)

Thurs / 6
Travel to Shiretoko National Park
Where is a good place to stay?

Friday / 7
Visit Shiretoko National Park
Where is a good place to stay if we have an early flight from Memanbetsu the next morning?

Saturday / 8
Return car and depart from Memanbetsu Airport