It is *not* about three different families, it's about one family living in different households. Explaination:
Jay has two kids, Mitchell and Claire. Mitchell is gay and has a partner; Cameron. They adopted an Asian baby girl, who is absolutely adorable, by the way. Claire is married to Phil, and they have three kids; the oldest is a typical teenage girl, the middle daughter is a studious 13-year old, and the youngest is a typical about 9 or 10 year old. Jay divorced his first wife and married a much younger woman from Costa Rica/Puerto Rico or somewhere. She has a son from a previous marriage, around Claire's son's age.
It's very funny and has won several awards.