INTP's are terrible actors. The underdevopment of F usually means that people can see through you when you fake empathy that a someone who is an F type would actually feel.
People arnt going to call you on being fake and not actually caring about what there saying, but they wont enjoy your company as much as they would someone who is actually feeling what there saying.
Im very quite around her family and I come out to be very unfriendly.She tells me alot that im heartless.I think I make her uncomfortable when around her fam cause im so quite
I used to be the same with my ex's family and It sucked, I tried to talk and act the part but it was just terrible for me. I would be awkward around them and way too quite, my ex hated it of course. It was so weird because im so cool in every other situation, just them for some reason. I thought i had to censor myself too much.
You can try all you want to act in such a way or another, or to get your confidence up and act like they do, but you wont succeed. You have to be sincere because your Fe function is so underdeveloped your acting will always be shit, you have to stop caring what people think and pursue the path of individualisation.
Carl jung used to take special interest in patients who did not adapt to society, who couldnt be moulded by some social caste. In his work he explains how it is important for these people to follow there own vocation and develop themselves in there unique way. In an interview with him he describes a day which he suddenly awoke to himself (not literally) and how it felt like he was walking out of some strange mist and decided that he would be an individual.
The majority of people in this world are Extroverted, so base value only on things which come from objective reality, things that are real and tangible. An introvert draws there value subjectivly from inside, they dont have this drive for sweet cars, working 9 to 5, popularity and a house. But to be percieved as higher status these are things you must acquire, so what hope does a Introvert have to feel confident and gain high self esteem?. You need to truely base your values subjectivly and be free of these inferior extroverts opinions.
Without going into this too much, I think you should let go and stop caring what people think and trying to be someone your not to make other people happy. Assert yourself. You'll find that when you stop caring everything will just work out. But you shouldnt even care if it does or not, because your being yourself and following your own vocation.