The rcswitch protocol is decoded in software, and decoding 2 data streams at the same time is extremely difficult.
It might be possible to do it using interrupts , but that would require a new rcswitch library.
I opine that it's not much harder than doing one at a time - it ain't rocket surgery, and as long as you're either using interrupts and/or calling the handler fast enough, I'll bet it isn't much more complicated (I'm thinking about when I implemented my own OOK RC protocol, and how much harder it would have been to add a second input - the answer is not very). Issue is that the rcswitch library is not built for that use case, and would need significant modification - I don't think the modification would be hard, per se, but you'd need to grok the code first, and OOK tx/rx code is usually somewhat challenging reading material.
You could run two receivers into one pin using an OR gate.
No you can't, because OOK receivers have AGC and adjust themselves to have ~50% output duty cycle with the given input. This is something you need to account for in your protocol (part of why the code is often weird), but it also means that any receiver not getting a signal is streaming gibberish with a 50% duty cycle, so anything you ran into the same pin through an OR gate would get OR'ed with garbage.