Q. Dear Rabbi. Should one avoid marrying a woman whose siblings are not Frum, if she is the right person and has all the qualities one needs and wants?
A. Talmud (Baba Basra 110a) teaches that before one gets married, he should check on the brothers of the woman he wants to marry, since most of the children to be born are similar to them.
However, Poskim omitted this Halacha, since it is considered only a “Mitzva Min Hamubchar” or a better mitzva and not an obligation. (Maharam Brisk 1: 130, Hanisuim Kehilchosom 2: 20 and others).
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit'a