> What is the probability that you are sharing the same birthday with people around you?

If you're a twin and your twin sibling is standing next to you, nearly 100%. But not exactly 100%: there have been cases of twins born on either side of midnight ending up with birthdays that differ by a day. (I don't personally know of any twins born on either side of midnight between Dec 31st and Jan 1st, who would then have different calendar years in their birthdays, but odds are very good that it has happened at least once in human history).

twins born mid flight as plane crosses time zone, can the second twin be born before the first!!?