The Poisoned Garden by Phill Featherstone

The ancient city of Chamaris is governed by powerful families. Chief among them is the House of the Leopard, headed by Lord Karkis, the Master of the City. Karkis is ageing and going blind, and he must look to his succession.
He has two sons. The elder, Ragul, is the child of his first wife, Vancia. The younger is Peglar, who is two years Ragul’s junior and whose mother is Karkis’s number two wife, Chalia. Karkis and Vancia also have a daughter, Malina, but in Chamaris women are the property of their menfolk and have no rights of their own, so the estate will go to the boys. However, the division may not be equal and will depend on their father’s view of their relative merits.
In order to inherit, Ragul and Peglar must qualify as adult citizens, a tricky process which involves successfully meeting three gruelling challenges of strength and courage. Ragul completed his some time ago, and now it’s Peglar’s turn. But whereas Ragul is sturdy and athletic, Peglar is bookish and not good at physical pursuits. He is reconciled to failure, until he receives help from an unexpected quarter.
After Peglar succeeds at the challenges he and Ragul are on equal terms and both are eligible to inherit the family fortune, but which of them will get the biggest share?
Peglar meets and befriends Yalka, a poor girl from the slums. She is like no one he’s met before, and with her help he begins to see shortcomings in the luxurious life he’s been brought up to expect.
Both boys set out to impress their father, and both take different routes. Peglar seeks the help of Yalka but Ragul takes a more direct approach. Meanwhile Ragul and Malina devise a cunning scheme to disgrace Peglar and disinherit him. There can be only one winner.