Only thing not adding up is that the cerberus owner can eat multiple fruits, because that theory just died this chapter.
BB can eat multiple fruits because of another reason, probably because he's so fat
BB can eat multiple fruits because of another reason, probably because he's so fat
I would speculate that a person can only eat one Devil Fruit because it connects with it's user Soul, if Teach have more than one soul living inside him he would be able to eat more DFs.
Now I don't know how Oda is introducing something like this lmaooo