Neither of them are in the sealed chamber.
Mewtwo isn't found in Emerald at all. You must trade from FireRed or LeafGreen to get a Mewtwo.
As for Mew, the only possible way to find one is by getting the Old Sea Map. The only way to get that is through hacking, since the long gone event was only released in Japan.
Good luck with getting them. Hope I helped!