Juvenile book I read in the seventies dealing with social issues of the time

Father is a traveling salesman. Mother is a stay at home mom. Oldest son is a college student who is physically not attractive but has a great heart. He has a black roommate and friend and gets a girlfriend for the first time in college. Oldest daughter is beautiful but superficial and self-centered. She and her best friend have a business of hosting children's birthday parties. Youngest daughter is plain but very intelligent. Youngest daughter's best friend is a handsome young man who is intelligent and is a clown for children's parties. Mother's sister is divorced and lives alone in the city.

I think you're looking for Who Wants Music on Monday? by Mary Stolz.

Thank you! Yes, this is the book I was looking for!