New PC for the parents is weirdly slow and idk if it's the unbranded SATA SSD Best Buy stuck in this thing probably being a DRAM-less piece of crap, the wifi chip I bought being 2.4GHz only and 2.4GHz being a lot slower than I remember, or a mix of both.
I tested the same wifi chip connecting to my phone's hotspot three inches away from it and it was getting a much more reasonable 25mbps down. So I've decided it's the antennas. It's one of those super tiny USB WiFi things, same size as a wireless keyboard or mouse receiver. I guess it just doesn't have enough power to reach the router in the garage with any good consistency.
I've ordered a chunkier unit that cables out to a pair of antennas, parents will just have to Deal With It sitting somewhere nearby. This new wifi deal will also support 5GHz so if the issue is actually interference on the 2.4GHz band that'll also become a non-issue.