in most ways I've seen it described, shikigami is more a status or state of being rather than a unique creature in and of itself like any other youkai or kami would be. abe no seimei was said to have actual gods/kami as his shikigami, for example.
so it is absolutely believable that the swords are tsukumogami, but at the same time bound to the saniwa as the saniwa's shikigami.
Re: TOUKEN RANBU
in most ways I've seen it described, shikigami is more a status or state of being rather than a unique creature in and of itself like any other youkai or kami would be. abe no seimei was said to have actual gods/kami as his shikigami, for example.
so it is absolutely believable that the swords are tsukumogami, but at the same time bound to the saniwa as the saniwa's shikigami.