Yup (he wrote, grammatically) number 2 is correct for several leavers, whose assembly it is.
Strictly, it should be St James's Street, as with all singular nouns ending in 'S', though I doubt whether Westminster Council has it as such on street signs, and few people bother to write Jones's rather than Jones'. and St Andrews, home to the Royal and Ancient Golf Club, is always written without an apostrophe. The Club and local people insist upon that, but what does the Club know of rules?