I read this book in the late 70s/early 80s. It featured a young girl maybe around 10 or 12 years old, only child, who moved with her parents from the city to the country to take care of her younger cousins whose parents were in a car accident (or something like that – maybe one was sick and the other was with them?) They all moved into a big rambling old house that her dad had loved as a kid. The girl wanted to grow up to be a writer so she picked the garret room that had a skylight over her bed. Initially she resented having to move and share her life with her cousins. Over the course of the book she grew to love them. She had a friend whose parents owned a bookstore. She loved the bookstore but her friend wasn’t thrilled with it. At one point in the book, a cat had kittens in the big old house and the bookstore girl fell in love with a fluffy black one she named inky. She wanted to keep it but her parents said no (allergies maybe?) so the main character girl kept it so her friend could come over and play with it whenever she wanted. I think at the end of the book the parents were well again and could take their kids back and the girl was sad that they were splitting up. I think her parents decided to have another baby? I might be making that part up though lol!
Any help would be appreciated! Thank you!