Fix issue with 2 independent lights on single source

I inherited an electrical conundrum. In particular, two hallway lights on the main floor and upstairs, sharing a circuit and each independently controlled by two switches, both on the main floor.

The main floor connections were a mess. No box; other than BX at the ceiling everything (cabling, switches) was surfaced mounted. The legs to the two switches were particularly unpleasant: flat nailed-in weathered 18/2 LVT cable running across walls and ceilings, not to mention some dead wires etc. Just a maze, so I decided to rip it all away and start over.

I knew what I wanted, and perhaps what the previous owner had tried to wire. Two hallway lights with independent 3-way switches. I planned to use wireless relays at the fixtures.

Upstairs was a snap even for an amateur like me. The short was just due to some fraying on both the hot and neutral. Cleaned up the 14/2 in the ceiling (shorted due to frayed wires), attached them to a wireless receiver I squeezed into the electrical box, connected it the fixture and put a pair of switches/transmitters upstairs and downstairs. Worked fine.

Next, I ripped out the LVT and switches. Should have paid more attention, because of course when I disconnected the switch for the upstairs light I opened that circuit.

I had envisioned the existing wiring to look like (switches & connections to fixtures omitted)

But of course that would not have made it possible for the main floor switch to control the upstairs light. Belated Duh!

At this point, the wiring to the old switches is irrelevant since they’re being replaced with relays at the fixtures. But I’m having trouble figuring out what the real (hidden) wiring is, and more practically how to energize the upstairs pair with the existing cables if possible.