The best decision you can make is to FORGET about business school as an end. It's simply a means.
I know it's hard for prospective applicants to understand this, but DO NOT PLAN YOUR LIFE AROUND GETTING INTO BUSINESS SCHOOL. It is foolish. Business school isn't some glass slipper in your Cinderella story. It's not going to transform an ugly duckling into a prince (or princess). It's a nice-to-have, a dessert, a cherry on top, and not some golden ticket to some life you were dreaming about. Because if you really truly believed that b-school is a "nice to have", you wouldn't be trying to make choices based on "how will this look to some random b-school adcom?".
With what you're faced with, if you feel that you will grow a lot professionally and personally by going to Poland and working for your grandfather, it could be great for your life. If your grandfather is putting you in a good situation (it doesn't always happen with family businesses) where you are given a chance to really develop some big responsibilities that you wouldn't get had you not been a relative, then it could be a great thing -- especially if you also get along with your grandfather personally. You can get some mentoring about how to run a business in a manner that few young people could get - and also from a far more personal standpoint than just a "mentor". But again, that depends on the nature of your relationship with your grandfather, and what kind of person he is.
It sounds like you are excited and curious about this opportunity to work in Poland with your grandfather. If so, follow your gut instinct and take it. Whether it's a great opportunity or a bad one is only something you can make a judgment call on. Don't let your choices be dictated by trying to impress someone in the future (in this case, a b-school adcom). Do what's best for yourself and your career first and foremost - again if your instinct is telling you to take this opportunity and you feel excited about it, LISTEN TO YOUR INSTINCT! As a younger person, it's harder to trust yourself, but you will learn that in many cases where there isn't a clear right or wrong (which is most things), it requires a judgment call and you just have to make a decision based on your hunch or your gut. There are people out there who will sit on the fence forever, analyzing everything to death -- and end up becoming indecisive to the point where they are paralyzed with fear of doing anything. Don't be that person. Now, if you're asking how adcoms will see it -- it's irrelevant. Adcoms take all kinds of people. What people are attracted to are those who are decisive, insightful, and engaging - and you only get there if you are fully committed to the choices you make (while learning from your mistakes in the process). Make career choices that allow you to grow and learn. Go into job situations where you are in a position to succeed (the family biz can cut both ways depending on the family involved and situation; it could be a no-win situation, or it could be a great opportunity). Do that, and b-school will be just a small pit stop in a long career - and not something that you're desperately clamoring to get into as your lifeline out of whatever life situation you're in.