Unexplained Latency, please assist.

I'm running two separate game clients in my house on two separate PCs. Both run the same client (download from war-mane website) & use the same WiFi. So basically I play with a family member a & we are both on the onyxia server.
The problem is that one of those computers is constantly between 200-400 ms & the other is getting an excellent steady 70ms.
I am stomped, I've tried everything. Re-installed game from scratch, reset network settings, check if its add-ons related etc. etc. etc.
Nothing is working, still getting 200-400 ms while the other PC is getting 70ms.
Both PC meet the minimum req for the game,, so that is definitely not it.

If anyone can help please do, I am losing my mind.

I think warmane limit some users connections to their servers! this problem is not of our ISP or Computer as you told us! because you are using same ISP in same place with 2-3 PC! warmane staffs don't have good answer for our problems and just say it's your problem not us!