Helena: Queen Victoria's Third Daughter is by royal biographer, John van der Kiste.
The Last Romanovs: In Their Own Words by Helen Azar
You do not need to own a Kindle to read these books. If you have an IPad, other tablets, or a Smartphone, you can download the Kindle app from the from Apple or Google Play. The app is free.
I have the Kindle and Nook apps on my IPad. Neither of these books are available in printed word. Bummer.
Kindle books are geo-blocked. If you live in the USA, for example, you can download only items on the US Amazon site. Americans cannot download books from Amazon.co.uk's Kindle site.