Disney does NOT NOT NOT own the previous 6 films. They only have the rights to future films and to the characters themselves. They cannot do anything with the older films.
I thought Fox owned Ep. 4 in perpetuity?? no?
So I don't think this is true. Fox owns the distribution rights, which will eventually expire, according to this. While originally Fox also owned the copyright to 'Star Wars', this was traded to Lucasfilm sometime in the late 90s, probably in the deal that netted Fox distribution rights to the prequels. And if you check out any 2000+ release of 'Star Wars', it will be (c) Lucasfilm, not 20th Century Fox. Zombie wrote an article about all this here.