Could the master’s of the slaves have sexual relations with them without their consent too? Shouldn’t it be obligatory for them to get married first?

When a male master owns a female slave, the female slave would by default become like his wife. She becomes lawful to him and they can have legitimate children. When a female slave would get pregnant, she would gain status in society, and if she as a child from her master and her master dies, she automatically gets freed.