As much a disadvantage as an advantage. It depends on their relationship. Will they concentrate less, will it make it feel like less of a Major for them? As a fellow pro, obviously I'm not, I would not be worried by them being paired but I get your point.
They seem like they’re best buds as well as sisters so they’ll definitely get on, and I’m sure they’ll be very professional re ‘advice’ etc and firstly each will want to win for themselves
Just wondered if I’d be calmer/better composed & more likely to perform better if I’m playing in an important comp with my 'bessie mate' beside me (as opposed to say putting Books & Bryson together at their US Open)?