Netflix vs My computer

My sister is on Netflix using some wireless box to stream , I have a download speed of 16 megabits, the download speed it not an issue but when my sister is on netflix and I am playing games (Via powerline adapters) my ping goes: 20-30-110-180-60-20 Which results in my game freezing and playing freezing and playing, is there anything on the router options that I can use to limit My sisters Bandwidth/ Or to get more stable Ping?

I have the latest BT HomeHub Router and the best package without going fiber optic