I haven’t been able to locate Jane Feather’s A Widow’s Kiss about the Mallory sister’s mother, but these two book about the sisters stand out as great books!
Although I am not usually a fan of Elizabethan romances with heavy courtier/political subplots, I thoroughly enjoyed both of these books. Wonderful characters, great tension and fanastic love stories make the subplot exactly what it should be: a backdrop for great romance.
There is a lot of history about the intrigues of court, first when Mary is imprisioned and then when she marries Phillip of Spain and has Elizabeth imprisioned….so history buffs will enjoy the characterizations of real historical figures. She has snappy dialogue that is not weighed down by an overattention to historical accuracy (in terms of grammar and spelling). Family is also a central theme, which personally is something I enjoy to help balance out heroes and heroines.
Both plots features crimes against women and the children they bear, and with feisty female characters its fun to see how the maneuver the dangerous political intrigues.
Having started another Feather series, (Duncan series from 1906s suffragette London) I look forward to adding this author to my retinue of standbys. Check her out, history buffs won’t be disappointed and its a good change up from standard hist-ro Regency fare.
Regency Reader 
Ugh…I detested this series. Feather is an auto-buy for me, because when she’s good, she’s really good, but when she’s bad, she’s really bad. The first book of the series (The Widow’s Kiss) was alright, but the following books, the stories of her daughters? So cold and icky. The history was excellent as always, but the romance was so tepid, I can’t help but feel Feather can be better suited to writing romantic historical fiction rather than historical romance.