My husband has two sisters and a brother who are triplets. I have the brother pretty securely typed as ENFj. One of the sisters I am at least 85% sure she is ISFp. The other sister...I'm having trouble.
I've mostly been waffling between INTp and ENTp, but INTj is also a possiblity (but only if my father and my brother-in-law are ENTj's instead of INTj's as I initially thought), or maybe even ISTj or ESTj. Actually, as I've been writing this post, both of the last two possibilities are starting to make more sense...
The two sisters are really close. They did everything together all through school, and roomed together in college. They've traveled out of the country together, etc. etc. They have pushed each other to do things that the other would probably never have done without the other.
All this makes me inclined to say they are Duals, but when I mentioned that idea to my mother-in-law, she disagreed. Though, she doesn't really know all that much about Socionics or Duality, just a very little bit as I have tried to describe to her. But then, while she may not know Socionics as well, she does know her daughters much, much better than I do, so her opinion is definitely worth lsitening to.
The sister whom I am still trying to type, got married over a year ago. The ISFp sister is still single. NTR, but... According to my MIL, shortly before the one got married, the other said to her mom something along the lines of, "I'm glad she's getting married first; I think if I had married first, she would have had a lot harder time with it than I am."
The sister in question worked very hard and excelled in school. She was very bookish, loved to read. She was apparently very inclined towards the sciences and worked on a Biology major for a while before switching to and graduating in Linguistics.
One time, a year after I married my husband, she and her sister and I all had summer jobs at the same water park. One morning, she asked me if I could pick her up that evening when she was done with work (I was on a different shift). I agreed. But the day was long and busy, and by the end of the day, I forgot to pick her up. She found another ride home, but she was quite upset with me for a day or two. I felt bad that very same evening when someone mentioned the situation, and I of course tried to apologize to her right away. She did not accept my apology right then and said that if I really loved her, I wouldn't have forgotten to pick her up, and she left the room still fuming.
We've had better interactions since then. Once last summer, she and her husband were up here, and we all went camping together. Once, she and I went canoeing together and had a nice conversation. One thing that stood out to me for some reason was when she confessed that, while she's always gone along with her dad and sister water-skiing, that she does it because she "knows it's good for her," but that she can't help thinking the whole time she's up on those skis, "I'm cold I'm cold I'm cold I'm cold."
She has a baby. And before the baby was born, she read all sorts of books giving advice on how to care for a baby, how to get the baby to sleep on his own, how to breastfeed, etc. Then she took what she considered the best ideas to implement into her parenting style. She was particularly passionate about the idea she read in one of her books, that she was never going to have her baby sleep with her; that according to the author of the book, that as long as a baby never slept with his parents, he would never know anything different and so would be much happier and easier to get him to sleep on his own. Even when she brought the baby camping, he had to have his own bed. (whereas I just would've been more worried about the baby freezing, and would've figured that one night with me wouldn't hurt anything).
Actually, you know what, I think I might be almost ready to settle on ISTj for her...but, I'm staying open to other ideas.
Her husband is either ISTp or ISTj. I've been thinking ISTp for a long time, mostly because I believe my FIL is ISTp and I think (and my SIL actually agrees) that they are the same type. But, maybe I have my FIL typed wrong. Or maybe (probably more likely) her husband and my FIL are quasi-identicals who just seem to have the same type.
Then, it comes back to her relationship with her sister. ISFp benefits ISTj...which, actually, seems semi-plausible. My MIL has observed that the ISFp was always the clear leader in the duo. And it might also explain why she believed that she could handle being alone after her sister married better than her sister could have. My MIL has also observed, that since she has been married, my SIL actually seemed a little relieved to be "free" of her sister in a way. Though, the two are still close, only now there's a husband and a baby between them.
Wow. Okay. I think I might have answered my own question...