Elsie J. Oxenham 
Strangers at the Abbey [EPUB ebook] 

“Joy, the queerest thing!” Joan put down her mother’s breakfast tray and stood gazing at her cousin.
Joy looked up from the letter she was reading. “What sort of thing? Come and have your brekker. What’s happened?”
Joan poured out a cup of coffee and sat down. “Mother’s had a letter, and she let me read it. It’s from somebody called Belle Reekie. Joy, I’ve got two new cousins.”
Joy stared at her. “You’ve got me, and don’t you forget it. I never heard of any other cousins.”
“Neither did I. But Belle Reekie seems to be one, and she has a little sister, so that makes two. Two cousins, and I’d never heard of them!”
Joy pushed away her plate. “Joan, what is all this about? We’ve known my family history, but you’ve never had any. It was just you and Aunty. Now you go and produce two cousins! What has Aunty been doing? Why has she concealed them all this time?”