What problem are you actually trying to solve? Do you want to connect any of the devices together?

7 items on arp in subnet show up as at least mac level on this host.

What the .11 is we don't know but you can follow mac octet to brand.

I would like the systems to be able to contact each other, and learn some network diagnosis in the process.
In particular I want the Windows system to be able to reach the Linux system.

I don't know what the .11 system is. It doesn't show up on scanners on iOS or Android. I don't think I have the MAC for it -- not from arp -a at least.

Ugh. Today only the Android phone can reach the Linux system. Windows can't, as before, but now iPad can't either.