To be fair,the exact meaning of the word from "absorb" to "acquire" probably ins't something that a moderatot would deem fit to re edit,since the meanings are similar to each other and they might have not thought of this situation.Well,just mentioning this for the sake of covering several scenarios.Since you treat them all as similar further down,let's go with that. Teach's case is split into two parts: 1) How he can steal devil fruit abilities. 2) How he can house two abilities in hi body at the same time. The "Yami-Yami fruit is responsible for both" attempts to attribute both parts to the darkness fruit,as the description suggests.The "many people in one" theories attempt to attribute only the 2nd part to Teach's special physiology,whatever that may be.Like I've said before,a theory that talks about just the 2nd part is not one that I would consider a complete theory as far as the subject of Teach in general goes.However,in such a theory,anything related to the 1rst part,doesn't affect the theory in any way.I'm not in favor of the darkness fruit being responsible for everything because then a dual ability wielding user would most likely had appeared before Teach. Honestly speaking,the way that this theory suggests isn't actually unique to Teach either.The suggestion that the 3 people are brothers explains why the 2 would be willing to exist inside of darkness,but it's not really limited to brothers.Good friends or even just people with the same goal could have done it.So with that in mind,a dual wielding devil fruit user should have appeared in the past as well if all it takes was just a mutual agreement between the people involved. In any case,I personally believe that the darkness fruit theories explain the 1rst part and the many people in one theories explain the 2nd part.In other words,a complete theory about Teach for me,would be a hybrid/combination of the two types of theories.The reason why I like this theory as far as the 2nd part goes,is cause it explains the small details like Teach's teeth. If what you're trying to say is that this theory doesn't cover the entirety of Teach's case,I would not disagree.Admiral has even said so himself in one of his comments on this very page.But if you want to say that the lack of mention of the 2nd part somehow affects this theory,I would have to disagree.How the abilities are extracted doesn't affect the way to house them.You yourself stated that Marco commented on Teach's special body as if he knew about it even before Teach got the darkness fruit.That should hint that whatever way according to which Teach's body is special,applied even before he got his ability to steal fruits.