[@Dead Cruiser]: Uh... Tiamat is still alive, and is in fact one of the leaders of the Reclamation of Chaos; it is led by Jörmungandr, Apep, Tiamat, Vritra, Typhon, Yamata no Orochi, and Aži Dahāka, seven ancient serpentine spirits that were born from the fragments of the Primordial Chaos. So if Tiamat is the one you want to reassemble, that wouldn't work. However, the Reclamation is trying to reassemble the Primordial Chaos, which is reasonably similar to what you're going for. In addition to fighting angels and demons, the Reclamation is trying to find, and either recruit or devour (if recruitment isn't possible) other spirits of chaos, and gather souls in general, to feed them into a cauldron of souls and further the rebirth of Chaos.

As for the other mythological figures you listed, no, they shouldn't all be children of Tiamat, as the various different pantheons of the world have all developed independently. Some of them could have been born from the fragments of the Primordial Chaos, which is a cross-cultural thing.