two diferent JR pass on the same trip

i a travelling to japan for two weeks
day 1 hakata to hiroshima
day 6 hiroshima to osaka
day 8 to osaka to okayama

day 8-day 11 will be at a ryokan no need to travel
day 11-14 okayama to osaka
day14 osaka to kansai airport

can i buy a 8 day jr west sanyo pass for my first 8 days and then

a 4 day jr kansai wide area pass for day 11-day 14

For the passes you can buy in-country, you can buy one or each type. If you buy them outside the country you can buy more than one, maybe only 2 of each....

I think you need to buy an exchange order for one pass in your country and another pass in Japan. There is "one pass for one person for a visit" rule with JR West Passes.

Yes you can buy both of those passes on the one trip.

However, individual tickets will probably be cheaper than the Sanyo Pass unless you are doing lots of long day trips from Hiroshima.

Hakata - Hiroshima = 8,900 yen
Hiroshima - Osaka = 10,000 yen
Osaka - Okayama = 6,000 yen

Total = 24,900 which is 5,100 yen less than an 8-day Sanyo Pass.

Also, it makes more sense to save even more and do:-
Hakata - Hiroshima = 8,900 yen
Hiroshima - Okayama = 6,000 yen
Activate JR West Kansai Wide = 7,000 yen.
Use it to go from Okayama to Osaka and back to Okayama.

Total = 21,900 yen. Saves you 8,100 yen.

Then activate a second JR West Kansai Wide to go from Okayama to Osaka and around Osaka and on to Kansai Airport.

Note that if you plan on using two of the JR West Kansai Wide passes then you must purchase at least one of them outside Japan.
ie you can buy two in your home country
or you can buy one in your home country and one in Japan
but you cannot buy two in Japan.

Hope that makes sense!

Enjoy your trip!

Thank you everyone for your help.

Are there any restriction on the number of jr Kansas wide area pass that I can buy per pax per trip?

I am traveling in a big group of 30 with 28" luggage each. Should I reserve seats? Are there reserve seats on the hakata- hiroshima- Okayama-Osaka line?

If buying individual tickets can I buy in my home country or when I get there?

Thank you in advance for your help.

First, You must know which pass to use. Kansai Wide area pass is not valid in Hakata and Hiroshima.
http://www.jr-odekake.net/en/jwrp/

-Should I reserve seats?
Yes.
-Are there reserve seats on the hakata- hiroshima- Okayama-Osaka line?
Yes there are.

-If buying individual tickets can I buy in my home country or when I get there?
Also note that you can get 10% group discount when you choose indivisual ticket. You must apply for it 2 week ahead of the date of travel though.