To piggyback of what neidu3 said, I think your issue is a wonky application of consumer hardware.
You can utilize your existing cable runs, but I would: -grab gigabit 4-8 port switch (a cheap Netgear 5p would work) -grab 2 access points (I’m a fan of Uniquiti, the nanos can be fairly inexpensive, especially older ones, these work as well). Make sure they include POE injectors (ubiquitis do)
Install the switch where you have AP1 and mainline that to your router (red wire), run an AP and the blue line to AP2 off the switch. Connect the POE injectors inline from the switch to the 2 APs. Bonus points if you want to add a 3rd AP at the main router (disable wifi on your router).
Uniquitis are pretty rad in that they’ll automatically select the best channel and power level to operate on give the density within your house as well as minimize interference from neighbors operating on the same wifi channels, and they’re self managing to a certain extent.
The biggest point is that you want to avoid chaining through devices as much as possible to minimize latency and throughput. Switches are especially designed for this application, while chaining through devices will absolutely impact performance. The ideal topography is wheel-and-spoke, where every device has a minimal hop path back to the router (router -> [optional switch] -> dedicated line to each AP/device). While you can rig an old router to act as an AP, especially with open firmware like openwrt, it’s still kind of a hacky way of going about it.
Edit: for reference, here’s my topography:
Granted this is quite a few years of collecting hardware when I spot deals or get old devices from friends (Though I’m not sure why my proxmox and pinhole are showing off the router, they’re connected to the switch).
Yup, I have my Unifi gear for the automated allocation like you said, though I think pretty much every SOHO manufacturer does this to some degree these days.