Incorrect Answer.
The formula 
x y (S(x,j) 
S(y,j) 
O(x,y))
- "decompiles" into 'For all x and y,
if x is John's sister and y is John's sister, then x is older than y'.
- More elegantly, we can re-express this as
'Any of John's sisters is older than any one of them'.
Evidently, this is not expressing that one of John's sisters is older than
another. (Why? E.g. what if John has no sisters?)
Note that the formula above
would make more "sense" if O were interpreted as "likes", in which case the
formula would say, 'All of John's sisters like each other'.
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