Gwynne's Grammar Test - Restrictive and non-restrictive postmodification

OK, I needed to sort this one out in my head, but think I'm there now!  Warning - this is one for true nerds and I don't really understand what it's doing in a general grammar test.

This question appeared in Gwynne's grammar test (http://www.telegraph.co.uk/education/educationquestions/9987757/Good-grammar-test-can-you-pass.html) and reworded in The One Show's grammar test (http://www.bbc.co.uk/news/magazine-22512744).  There has been a lot of fuss online about it, so let's see if I can shed any light on it.

"I should like to introduce you to my sister Amanda, who lives in New York, to my brother Mark who doesn't, and to my only other sibling, Evelyn." What gender is Evelyn?
1.  Evelyn is male
2.  Evelyn is female
3.  Impossible to know from the wording of the sentence whether Evelyn is male or female.

Interestingly the above wording appeared in the answer section, but the quiz now has a different wording, as has The One Show version:
" I should like to introduce you to my sister Amanda, who lives in New York, to Mark, my brother who doesn't, and to my only other sibling, Evelyn."

When a noun is postmodified the information can be additional information, in which case it is enclosed in commas and referred to as non-restrictive or non-defining, or it can identify the noun, in which case the commas are not used and the clause is said to be restrictive or defining:

• my sister, who lives in New York,  (the relative clause is providing additional information)
• my sister who lives in New York, (the relative clause is identifying which sister - the one that lives in NewYork)

In the sentence "I should like to introduce you to my sister, who lives in New York, to my brother who doesn't, and to my only other sibling, Evelyn." we can deduce that there is only one sister and the writer has offered the additional information that she happens to live in New York.  However, by omitting commas after brother, the writer is indicating that he has more than one brother and is specifying the brother that doesn't live in New York.  We can deduce that Evelyn is male and also lives in New York.

Without the inclusion of the names 'Amanda' and 'Mark' this question would have been much more straightforward.  However, our language also allows something called non-restrictive and restrictive apposition.  Apposition is a way of linking grammatical elements, where each element refers to the same thing:

•  Swansea, her home town, held a special place in her heart. ('Swansea' and 'her home town' are the same place)
•  Cheetah, my chimpanzee, stole the banana ('Cheetah' and 'my chimpanzee' refer to the same animal - sorry to stereotype on the behaviour front all you chimps out there!)

When punctuating, the rules are the same as they are for relative clauses.  If the apposition is additional information, it is enclosed in commas; if it identifies the first element, no commas are added:

• Mr. Northern, my teacher, will be at the meeting. (additional information - non-restrictive apposition)
• Mr. Northern my teacher will be at the meeting. (It is Mr. Northern my teacher who will be at the meeting, not any other Mr. Northern that I know - restrictive apposition.)

So the fact that 'my sister Amanda' does not have a comma between 'sister' and 'Amanda' implies that there is more than one sister, as Amanda here is restrictive apposition and is identifying which sister the writer is discussing.

In the first wording 'my brother Mark who doesn't' is very confusing.  Mark is restrictive as is the relative clause.  Perhaps that is why it was changed.

In the second question 'to Mark, my brother who doesn't' implies another brother because the restrictive relative clause is postmodifying 'my brother'.  So can we deduce another brother and another sister?  Quite frankly, I don't care.

Why on earth was this question included?  The only possible, sensible reason I can think of is to highlight the ridicuous nature of grammar tests!