Weird intranet lag spikes

Greetings,

Having a strange issue I'm not sure how to approach and would love some tips on possible paths forward.

My spouse and I game together inside our house via laptops. We occasionally play with people outside of our home. When either of us is hosting a game, people outside of our internal home network have no issue playing with us. But when we try to play together? Pretty frequent lag spikes. It doesn't matter which of us is hosting either. The other person will have pretty big spikes.

Both of our laptops connect via WiFi, usually 2.4 ghz. We have an archer c9 that's probably 7-10 years old. It has two 5 port switches connected to it as we try to have anything that can be hardwired actually using Ethernet. So aside from our phones, doorbell, and carbon monoxide detectors, nothing else is on WiFi other than our laptops. No QoS set up on the router. We do use a pi-hole for dns filtering of ads.

We have tried using both the steam Join Game feature as well as direct IP connections, noticing no difference. I even set up a dedicated server on a wired connection on a desktop, and while my laptop didn't experience latency, theirs did.

Their laptop is a windows 11 asus, whose drivers I have updated this morning to no different effect. My laptop and desktop have been some combination of Windows 10, Ubuntu, and Mint.

It absolutely blows my mind that people outside our network don't run into issues but us sitting on the couch together mere feet away can have so many problems. My next test is going to be both on 5 ghz, which I am sure we had to have tried at some point but I won't rule out because my memory is atrocious, and following that I don't know if it's time to break out wireshark or what.

Any thoughts?

Thanks in advance if you made it this far.