Whatever about the photographer, I'd sincerely hope the sister (or the now fiancé) ran that by Jen first... Given that she's usually abroad and all the family are around for the wedding, it does make sense to have a double celebration... But only if the bride is happy with that!!
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Ah no, unless the bride is OK with it (or at the very least aware of it, it's definitely not ok... Your wedding day is one of the biggest days of your lives, it's a massive build up and the couple are meant to be the stars of the show. The focus is meant to be on them for at least those few days, there's 51 other weekends in the year to announce your engagement.
I have a feeling Jen was on board with it and happy out for the sister though... She does seem genuinely laid back at times, and quite close to the sister too.