"Official site of Rurouni Kenshin movie states that who will be cast as Shinomori Aoshi and Seta Sojiro in the sequels is one of the most intriguing aspects of the production which means that THERE WILL BE AOSHI and SOJIRO in the next movies! Celebrate, people! RKnews can’t get better than that!
The site also states that Aoshi is pursuing Kenshin to avenge his fallen comrades while Sojiro is, as expected, Shishio’s associate famous for his speed in a fight. It also noted that the movies will be based on Kyoto arc so we are not to expect too literal adaptations probably."
The official website apparently also states that the original cast of the Kenshingumi will be returning.
And from AnimeNewsNetwork:
"The official website for Shueisha's Jump SQ. magazine revealed on Tuesday that actor Tatsuya Fujiwara will play the former government assassin Shishio Makoto in the two upcoming live-action Rurouni Kenshin sequel films. The website also revealed that Keishi Ōtomo (Ryōmaden) is returning to direct the two new films, which will be titled Rurouni Kenshin: Kyoto Taika-hen (Rurouni Kenshin: The Great Kyoto Fire Arc) and Rurouni Kenshin: Densetsu no Saigo-hen (Rurouni Kenshin: The End of a Legend Arc). The films are slated to open in summer 2014.
Fujiwara previously starred as Light Yagami in the two live-action Death Note films, as the titular protagonist in the Kaiji: The Ultimate Gambler and Kaiji 2 - Jinsei Dakkai Game live-action films, and as Shuya Nanahara in the two live-action Battle Royale films."
Official movie website (in Japanese)