Did they decide to use their middle or nicknames instead of first names?
Yes! (middle names) Are these middle / nicknames the same?
No, but OTRTDid they add suffixes to their full names?
No For example, II and III?
Did they choose identical images ( hair, style of clothing, manners )?
NoDid they marry twin sisters? Women with same first ( and middle ) names? And then had kids at the same time?
This will surely create a confusion in a maternity ward.
Great idea, but not thisDid they buy ( rent? ) houses at the same addresses in different cities?
This is suggested by the title... Not that, but the title does have relevance.Were they brothers in law?
No Imaginary brothers?
No Did they know each other?
Yes Were they prisoners?
No Is something like a paradox/loophole involved here?
No (e.g. they committed a crime ad said that one thought it was the other so that either of the two was really aware of the crime committed or directly faulty?)?
NoWas it evident at a first glance that they took such a decision?
No (for strict definition of "glance") If so, for instance from a label they needed to wear at work?
No From the way they introduce themselves?
Yes Were they married?
No Did they live in separate houses?
No Did one of the two take the decision as a consequence of the other's decision?
Possibly, but irrel Writing books relevant?
No (e.g. one was a writer and wrote a book in which he told a story from the point of view of his (imaginary?) brother. The brother in the book took the decision to be like his brother which in turn was the writer?)
No Had they be 3 brothers, would the puzzle work?
Possibly To be sure, M and J decided to "think" they were one the other right?
No, they knew who they were No third brothers involved?
Correct, it's just the two of them Did they take the decision for a limited amount of time?
No For years?
Yes, presumably Until something happened?
No In a quiz show?
NoWe said that the two decisions could have been independent one from the other right?
Right Did someone die?
No Are tombstones relevant?
NoWas it a joke?
Possibly (even likely) Did they have an advantage in thinking to be the other?
No