Hi there!
Here are some answers to your questions (as much as I can!)
Is it worth if I buy the JRP?
A 7 day rail pass is ¥28,300, so it would only make sense to purchase this if you spent over this on JR tickets. Here is a cost breakdown of your itinerary:
- Kansai airport > Toyohashi: ¥10050, (162mins, 319km)
- Toyohashi > Tokyo: ¥8700, (135mins, 293km)
- Tokyo > Kansai airport: ¥14800, (266mins, 613km)
TOTAL: ¥33550 for 3 legs
This means that I can recommend a JRPass for your trip.
Oh, the children are 6 years below so they are free, right? But can they have their own seat on Hikari, Kodama etc?
Yes - children under 6 travel for free on all JR trains. Provided their is no-one sitting in the seat they can use it on Hikari/Kodama and all other bullet/train services, however if the seat is reserved/needed by a fare paying passenger they should move to another seat.
Can I use the JRP too even I'm studying here? If can't, if there any other choices to safe budget or I have to buy normal JR tickets? So, I have to go through the JR gates and my family go to the counter check, is it?
Unfortunately the Japan Rail Pass is only valid for holders of the "Temporary Visitor" visa. As you will be in Japan under another visa class, the Japan Rail Pass will not be valid for use for you. For bullet train travel I'm afraid there is no other easy way to save money as discounts are extremely restricted to OAPs and tourists only so you will need to purchase tickets as you go. Where you do purchase tickets you would be able to go through the same side gate as your family and will be able to present your full ticket along with your families Japan Rail Passes to make things easier however.
Can I buy the tickets on behalf of them and send to here (Japan) ?
Yes, you can see our full delivery details here online.
Are JRP can only use on JR Lines only?
Yes, the Japan Rail Pass is valid for all JR lines and for the Tokyo Monorail. You can find full validity details here.
Do you have any recommendation on apartment for 8 people? It is really hard to find them :(
Now that is hard :). Based on experience you'll be better off going through a foreign agent, such as holiday rentals or airbnb. One thing for sure though, is that if you do go for this option you should be fairly prepared for living in close quarters - as you know Japanese flats are not the most spacious, so make sure you ask for some sort of floorplan sketch before you make your choice!
Hope this helps!