What EXACT setting should be used for two or more computers on the same network, downloading the same file(s) to QUICKLY download from each other?  Thanks for any and all help with this.

You can try adding local IP address and port of other client on both sides manually on Peers tab in torrent options.

If you share multiple torrents, you can add those peers in Options — Peers — Local peers. Clients then should try to make a contact on any torrent you add.

Or you can enable automatic SSDP discovery there if your devices are on the same broadcast subnet, and those broadcasts are not filtered by network hardware (say, wireless).

Note that bittorrent protocol does not say anything about “local” peers, and its piece priority and fairness algorithms consider them equal to any other. Application developers may add some logic about that, but it is not guaranteed that the behaviour of two local peers would be optimal. However, in general, with fast and wide LAN it doesn't matter that much.

Note that peers might already see each other via global address and port pairs. You might need to disconnect that connection (possibly rate limited by ISP).

What's more important, most peers won't connect to the same IP address more than once on the same torrent. So you won't get twice the speed, you'll get roughly half of the peers on one client, and the other half on the other. They might even start to affect each other negatively by not being able to talk to peers they need that are blocked by the other. Only in case of per port rate limiting by ISP (which is a bit too primitive and ancient) it can be better (but then you can just run multiple portable clients locally). Or maybe you have a super fast connection, and super slow computers that can't even handle the disk load.

To provide tangential info to the excellent answer above, the very old and practically unused feature introduced by uTorrent is "ISP peer policy" https://github.com/arvidn/libtorrent/discussions/6838  that allowed, in my opinion, connection and bandwidth prioritization of the specified IP ranges. However its usefulness died down without reaching wide adoption, due to ever increasing pressure on individual BT users and ISPs. I think it would do wonders if, as a side-effect of this feature, known LAN IPs always had higher priority by default. Tixati probably never implemented this. However, fear not, as long as you don't have a gigabit internet connection, your LAN peer should always occupy most of the channel for local transfers.

And if you allow me to propose a totally different solution to your problem: SMB or NFS for file sharing at home. A dedicated NAS server with all the storage as a hub for your data? SyncThing for cloud-like synching between your devices?