Is it legal to have two families living in a single family?

[Jin Zhang]

Hi everyone, I am a bit confused about the rules around single families. I am think to get a single family house and separate them into two units without significant structure changes. For example get a house with a livable basement meeting the requirements and separate them into two units with different entries and then rent to two families. Is this not legal? Would this get into problems with the city? From my research, this seems to be something being frown upon and might be a problem. However, for people who are househacking or sharing a house with multiple friends or renting out individual rooms, they have multiple families (although mostly one person household) living in a single family too. Is this okay? Or they are violating certain regulations too? Any input would be greatly appreciated! Thanks 

Jin