Eh? I think you might have confused the Magus Sisters and Anima. If you're in Baaj Temple, then you're trying to get Anima. In that case, then yes, you do have to get the destruction sphere treasures from Besaid, Kilika, Djose, Macalania, Bevelle, and Zanarkand Temples in order to break the seal.

I'm not too sure whether you can get the Bevelle treasure after you get the airship or not. I think you can, since it's not exactly easy to get on the first time throug. I doubt Square is going to leave you hanging like that.