I have 2 computers using the same wifi network at the same time

hello.

i am currently using 2 computers. one is a desktop pc. the other is a laptop. we both use the same wifi network. every time the laptop connects to the wifi network. i lag. i mean lag like a mofo. youtube vids take twice as long. it's even worse when the laptop is downloading.

i tired messing the the QOS settings but it didn't work. my internet provider is IInet as i live in Australia.

please can you help me not lag anymore as i am fed up