I'm working on a novel where the heir to the throne (Orion) is 11 years younger than his brother. The older brother (Rick) is very jealous of Orion, and wants to kill him for the throne. Rick and Orion are half-brothers with the same mother. Orion's father is the king of one kingdom, and his mother is the queen of a neighboring kingdom, so Orion will inherit both and join the two. Rick's father is nobody special, but Rick believes that his birthright has been stolen form him by Orion.
I need some ideas for conflicts between the two brothers that could be mistaken for accidents. One example I have is where Rick poisons Orion's drink, but it's not strong enough to kill him.
The story takes place in a medeval setting, where modern technology is just beginning to be introduced (the palace is just being upgraded with electricity and indoor plumbing).