Glossing over any reason of why this is being asked, I’m curious as to the naming conventions of Japanese clans during the Sengoku and Edo period, specifically for the surname. Was it common for all members of the clan to share the same last name? For men, women and children? How did intermarriage between the clans dictate which surname was used? Knowing that clans weren’t necessarily entirely blood relatives, how did those outside of the clan’s direct lineage name themselves? Any information is appreciated.
The only time a man would use his wife's clan name is if the marriage is a "marriage adoption," which happens when a family doesn't have a surviving male member, and so opt to continue the family by adopting someone and cement the tie/give him legitimacy by marrying him to a daughter.
When Nagao Kagetora was adopted to Uesugi clan, he took one character from the personal name of his adopted father (as was the norm) and became Uesugi Masatora. He later received one character from the shōgun and became Uesugi Terutora. Once he took his Buddhist vows (the second time) he became Kenshin. Kenshin gave his original name Kagetora to an adopted son from his erstwhile enemy the Hōjō clan, who became Uesugi Kagetora and ended up fighting and losing for the clan's succession.
You can also read here for some more information on Japanese naming convention, by /u/cckerberos.
See here on how females were named and addressed. Sanada Nobushige addressed his sister as "Muramatsu" in a letter he sent her. That is not her name, but the village she lived in.
Also for /u/CpKgunz