I know my dad is ISFp. I don't think they are duals.
Around strangers, she's quiet, almost never makes the first move towards people. But around her friends or family, extremely animated. She talks with her hands and is very expressive, wordy and can talk on and on about lots of things. Of the people in our family, she's by far the most extraverted person yet she may still be an introvert, I'm not sure. I sense that she's guarded with people she doesn't know but if they are the first to approach her, she's really friendly.
She always (and I do mean always) forgets where she left her keys, her purse, her sunglasses, where she parked the car, etc.
She's a great mother, conservative, upholds traditions, family is very important to her. She only had two kids but said she would have had more if there had been more money. Motherhood was her goal in life, I think. She was trained as a music teacher (vocal music was her major in college) so she did teach for awhile but didn't really like it that much and quit to be home with my brother when he was born. She still enjoys singing.
Dislikes interpersonal conflict but will engage in serious discussions (like politics, religion) and is willing to agree to disagree (which my dad does NOT like to do--he won't even engage in the conversation at all if it's controversial). She's interested in other viewpoints but it's not easy to change her mind about something even when you have a good argument.
Extremely positivist, not a negative bone in her body. Always turning lemons into lemonade (which is nice on the one hand, annoying on the other hand because I feel like she expects me to do the same).
Loves the beach, relaxing, hates to exercise, couch potato. Loves to laugh--has always enjoyed my dad's pranks (he's the ultimate practical joker--he used to pour cold water over her when she was in the shower just to get her reaction--he's ashamed of that now but it's a classic family tale), laughs really hard at him--they have a good relationship although they've had their share of problems also.
She's rational. Rarely cries (growing up I'm sure I saw my dad cry more than my mom). If there's a problem, she's the first to point out the facts and lay the situation out logically. Yet she finds complicated intellectual arguments hard to follow. She thinks she's dumb (she's not) and gives up too easily when it comes to trying to understand a concept or thought. Tosses her hands in the air and says "you all are too smart for me!" (annoying)
She's solid, emotionally (never falls apart the way my dad and I do). For example, if we found a dead baby bird in our yard, I might actually shed a tear or two and want to bury it. My dad would turn his head and get all sad. My mother would just say "oh, that's too bad! Well it happens, life goes on!" or something cheerful like that. She always tries to cheer me up by pointing out the facts "it is what it is" type of thing. And I always think to myself "yeah I know, blah blah blah, but that doesn't help how I'm feeling!"
I guess I would say that she's expressive, but only expresses her positive emotions. When they are negative, she hides them or just gets quiet. When my mom and dad would get into a disagreement when I was growing up, my dad would just tune out completely and my mom would match him in silence. So they would sit there saying nothing and we could always tell when they weren't getting along because of the quiet tension. I don't think I've ever heard my mother shout or yell. EVER.