ok this isn't really pick-up because normally i would just move on, however, here's my advice.
become best friends with your best friends sister, game her, throw loads of IOIs at her, spent time with her, get stuck in comfort (on purpose) she'll put you in the LJBFZ, and by that time she will have genuine trust for you, and her fears about you dating her best friend will be put to rest. how long will this take? it can be done in 3 days

Don't avoid at difficult situation (your best friends sister) take the challenge straight on, but just play it right

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My Journey to become a pick-up artist
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