No, Muzan Kibutsuji's canon wife and daughter (Rei and her child) from Season 1 of Demon Slayer were human, not demons, though they lived under assumed identities for his concealment; however, fan-created works (Fanon) feature demon daughters, but these aren't part of the official story.
Shiko Kibutsuji (鬼舞辻 死子, Kibutsuji Shiko?) is Muzan Kibutsuji and Enmu Kibutsuji's eldest daughter and the youngest of their two children. She is currently their only biological child.
Rei ( 零 れい , Rei?) was a minor character in Demon Slayer: Kimetsu no Yaiba. She was a human wife of Muzan Kibutsuji, who had assumed a false identity.
The main reason Muzan has a family. is to blend into human society. If you don't know, Muzan killed the woman's husband. and then became close to the woman. because her family is influential. You see, the Demon Slayer Corps. has been following Muzan for centuries. He did the most strategic approach.
He's been adopted by a wealthy couple without children of their own, who dote on him as if he were their biological son. The adoptive father runs a pharmaceutical company, suggesting that Muzan has infiltrated this family to pursue his goal of creating a drug to overcome his weakness to sunlight.
While on the verge of being defeated by the Demon Slayers, Muzan adopts an enlarged demonic infant form in an effort to protect himself from the dawn's light. He is approximately as tall as a 3 story building when standing up, has very pronounced blood vessels across his body, small claws in his hands.
Kaigaku was a former Demon Slayer and Zenitsu Agatsuma's senior disciple under the former Thunder Hashira, Jigoro Kuwajima. However, sometime during the Hashira Training, Kaigaku went on a mission and encountered Upper Rank One, Kokushibo, quickly surrendering to him to save his life and later becoming a demon.
Nezuko's immunity to sunlight in Demon Slayer may come from eating the Blue Spider Lily, as shown in the anime's finale. The Blue Spider Lily's significance adds depth to Muzan's failure, highlighting his contempt for humanity in the series.
In Chapter 205, we see Obanai and Mitsuri reincarnated and married, as they promised before they died, and they are running a restaurant together. In the volume extras it is revealed that they have five kids.
Also the reason why Nezuko was already so powerful is because Muzan injected tons of blood in her body and the others in hopes of creating a demon that could conquer the sun.
Nakime, Daki, Mukago, and Ubume are the only known members of the Twelve Kizuki who are female. Gyutaro and Daki are the only members who are biologically related to each other, as they are brother and sister. Kokushibo and Kaigaku are the only members who were formerly Demon Slayers.
Personality. Anne was a kind and loving soul and was described as the only person that Muzan had truly loved, besides his three daughters.
After accidentally consuming a drug created by Tamayo, Yushiro, and Shinobu that was deliberately designed to counter his abilities and weaken him over time, Muzan's hair grows in length and turns white due to the drug drastically accelerating his biological age.
Fun fact: nezuko's favorite hashira is sanemi.
Size Alteration: Upon being transformed into a demon, Nezuko displayed the basic ability to change and alter her body's size and height. She was able to shrink herself into the physical size of a small child in order to fit inside a small box or a basket, and she could also enlarge herself into a much bigger form.
Muzan has always been a rational character, but fans believe killing his doctor is the only time he regretted taking a life.
Twelve Kizuki. The Twelve Kizuki (十二鬼月, Jūnikizuki) is a special group of demons who serve Muzan and have a special mark of their servitude engraved on their eyes. Second only to Muzan, they are the most powerful demons to have lived.
Some time before or during Hashira Training, Jigoro committed seppuku when learning that his former protégé Kaigaku defected to gain the powers of a demon. According to Zenitsu, his death proved to be slow and agonizing since no one could cut off his head while he bled out.
Kaigaku, Zenitsu's former Thunder Breathing classmate, is the weakest of the Upper Moons. Despite his impressive speed and combat versatility, he lacks experience with his Blood Demon Art. He is placed as the current Upper Moon 6 after the defeat of Gyutaro and Daki.