Q: Is it true that according to Kabbalah it is forbidden to whistle inside a house?
A: Nonsense (There is no prohibition against whistling. Outside of Israel, non-Jews whistled, so Jews refrained from doing so. It is also permissible to whistle on Shabbat. Shut She'eilat Shlomo 1:182. This is also the opinion of Ha-Rav Yosef Soloveitchik. Divrei Ha-Rav, pp. 197-198).
Q: Is it possible by looking at a pregnant woman's fingernails to know if she will have a boy or a girl?
Q: What is the source that a pure silver knife is a Segulah for a livelihood?
A: There is none (And so says Shut Doresh Tzion of Ha-Rav Ben Tzion Mutzafi: It is a waste of money).