I have 2 ISFJs close in my life. One is my sister-in-law, and one is my admin assistant. We get along great, and it is always a very harmonious, caring, and mutually-supportive interaction. There are definitely some major differences, however.
Both are very literal people. My admin assistant is incredible faithful to instructions, which means a reliably consistent work product every time. It also means I need to remember she does not read my mind when I leave out little bits of detail or expect her to get my general drift about something. Thank goodness she has a sense of humor with me when I get too much in my head! As for my SIL, I get surprised sometimes when I say I want to do something or that I like something and it's just a fleeting impression in my mind that I quickly forget, and then she follows through on it.
Also, I find that they both like things. Especially my admin. She loves luxury goods and collects shoes, handbags, etc. My SIL loves nice jewelry in a major way. They both take gift giving very seriously. They give nice gifts at all appropriate occasions, and they expect regularly scheduled gifts from loved ones.
I think they are both more dependable than me. They are both extremely trustorthy and loyal people.
I tend to have more exotic tastes in things. I have more interest in trying weird foods, reading strange books, listening to ecclectic music, and collecting quirky friends. I am also more theoretical/academic than them, and I often tend to be the inspirer in my relationships with ISFJs. I often find them to be conservative in how they approach life, and I am more inclined towards bold choices.