1) is it every train depart from kokusai will direct connect to saikyo line or i need to check it before on board?

2) i got 2 results, quite confuse. i think every train depart from kokusai tenjjijo will stop at osaki for minutes, then direct going to ikebukuro, please correct me if i wrong
Kokusaitenjijo Map
Private Railroad Rinkai Line
Rapid 10/19/2009
09:57am
10:11am
[14min.] 8.7km 320yen
Osaki Direct
JR Saikyo Line
Rapid 10:12am
10:29am
[17min.] 13.4km 190yen
Ikebukuro Map

No, quite a few trains terminate at Osaki, where you would have to make a very easy transfer to the Saikyo Line, Shonan-Shinjuku Line or Yamanote Line.

or i need to check it before on board?

I personally would just get onto the next departing train. If it goes all the way to Ikebukuro, great. If it terminates at Osaki, I would make the transfer at Osaki.

About half of the trains only go as far as Osaki (i.e. Rinkai Line only). The rest continue onward on the Saikyo Line to Omiya or Kawagoe, and these all stop at Ikebukuro. As you can sometimes wait for up to 10 minutes, the best thing is to catch the first train that comes, and change at Osaki if the train terminates there. At Osaki, you can catch a Shonan-Shinjuku Line train from the same platform. You can also change to the Yamanote Line at Osaki (different platform), but they stop at all stations to Ikebukuro, so it is better to sit and wait for a faster Saikyo Line or Shonan-Shinjuku Line train.

- Kokusai-tenjijo Station: timetables: weekdays
http://www.twr.co.jp/jikoku/kokusai_h.html
- Kokusai-tenjijo Station: timetables: Saturdays, Sundays and holidays
http://www.twr.co.jp/jikoku/kokusai_k.html

In each of the two pages, the upper timetable shows trains for Osaki / Tokyo Teleport.
: Trains without signs are destined to Osaki.
: From 09:15 to 19:45 - Trains with signs are direct trains to JR.
: From 10:30 to 15:00 - Direct trains are Rapid trains destined to Kawagoe.