There is obviously not going to be a clear answer to this question, especially on the point of which pax is the problem. It seems clear to me the problem is the obese pax who is occupying more than his/her fair share of the aisle in in question. From a safety viewpoint, should this person be in the centre or aisle seat he/she is a hazard in an evacuation situation. He/she cannot have the armrest raised according to safety rules but may try to do so.
There is nothing hypothetical in this question and I do not understand why a clear answer cannot be given as the circumstances cited are perfectly clear. It seems one either accepts several hours of discomfort and potentially being trapped in the event of an evacuation without complaint or suffer the consequences.
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