Their mom and dad got divorced and they want them to get back together. But dad already has a new lady in his life, with another child their age.
He wants them to come visit them, but they refuse without their mom. So he invites her, too.
Scholastic sent me an ARC of this book to read for review (thank you). It has been published and you can get a copy now.
The sisters have different attributes so they argue. The new girl is nice but they aren't sure about her. And her mom is nice, too.
It takes a bit of time with problems here and there that make things difficult. Everybody has to change a bit but it ends happily.