I have been told that both are of the Tomari-te family. Wanshu as I have also been told was brought to Okinawa by a Chinese envoy who settled in the Tomari area. Not to sure about seisan but I will look to see what I can dig up from my notes. Both are practiced in the Shorin-Ryu I study as taught by Shimabukuro Eizo Sensei.
There are 2 versions of seisan both from tomari te school and naha te. Seisan means "13" meaning 13 techniques or 13 battles I am not sure. Where the kata came from I am also not sure I believe both of these kata came from China though either literally or based on a fighting style. Wanshu is from tomari te and your history is correct as far as I know.
The versions chinto01 would be practicing under Shimabukuro Sensei would be Kyan's seisan and wanshu.
Matsubayashi Ryu would have influence from Aragaki and Kyan
Matsumura Shorin Ryu would be Hohan Soken's versions with the differences done by Fusei Kise or Yuichi Kuda mainly.
Good luck in trying to find the truth on that. Both of these kata (as has already been mentioned) are already quite old and therefore it is quite impossible to say with any kind of certainty where and when they came about
Well that is easier. Most Shorin styles (and derivatives) have those (not sure if Matsubayashi ryu has Seisan). Also Wado ryu has some versions of those, as does Shotokan, although Shotokan uses different names. Seisan is, I believe, Hangetsu and Wansu is Enpi. Also, as has been pointed out, there is a "naha-te" version of Seisan also. In my opinion, both of these Seisan originated from the same kata, but have been changed during history. They look quite different, but there are also many similarities between the two kata