Well, that sounds like the silliest intervention ever! Interventions are supposed to be for people with REAL problems!
I recommend reading The Womanly Art of Breastfeeding, a LLL book, and finding a support meeting near you. I also suggest you tell your sister and bff to do the same - read the book and attend some meetings. Heck, in my town, the LLL senior leaders even post their phone numbers on the LLL website and mamas can just call with questions!
One of my tactics in avoiding other people telling me what to do is A. doing my homework, and B. talk about my decisions in the norm, despite it not being "socially accepted". So, when I said I was having a homebirth, I just talked about it casually as if nothing was odd about it. If I was questioned about it, I can easily mention the statistics that show c-sections are way out of balance here in the USA due to drug intervention. I can casually talk about the millenia of women who have been birthing in the bush before I was even born.
When I talk about breast-feeding, I have no problem saying I hope hope hope that my daughter breastfeeds for at least two years. It's all in the tone -- "well, obviously I'd want to BF for as long as possible, wouldn't you??" Not with an elitist tone, but what you are implying is wouldn't you want what is best for your kid for as long as possible?? And I've gotten very little resistance. If I get any "oh that's weird!!" kind of comments, I remind them that when a kid is 18 months, it's not an EBF baby. It will eat solids, but when it falls and bonks its head or wants to go to sleep, nursing is there to help them.
I've also found that using the "sleep card" works wonders. "Ew! You co-sleep! That sounds so dangerous! Don't you want your alone time?" And I can reply with, "Well, however my daughter falls asleep is how it's going to be because I
want to sleep!" This could be used for nursing for sure. Who doesn't love the power of the boob and the magic of nursing down?!?!