AAQ, if we judged people’s grandchildren or sons-in-laws, we’d have quite a lot to explain. Rav henkin was very anti Zionist. His grandson is the bnei bonim zionist/feminist. Rav chaim brisker said zionism is avodah zara; his grandson was rabbi yoshe ber; he also said when his son rav moshe was getting married, that “ich hob farliren a zun”, when the noshim paskened a kashrus shailah on their own at his wedding. Rav shach, who called Israeli democracy “cancer”, had a son who was a zionist.
Rav yochanan ben zakai’s nephew was the head of the baryonim.
Rav Moshe didn’t hold of any of the above deviances from Torah; he writes that women being taught gemara shouldn’t have to even be explained as it’s an open gemara. He also didn’t necessarily “choose” his son in law. He also would have been astonished at the opposition to metzitzah bepeh, and other innovations from his family. Gedolim’s personal family issues are not a proof as to what they hold. We can only go by their actual words and by talmidim who are mamshichei darcham. If you want to know what rav moshe held, you would want to ask rav bluth, rav dovid, rav belsky, rav nissan alpert, and other people who were very close to him.