Yup, Adam's got you covered
There's no problem at all with using a Y-splitter to feed two subwoofer with a single "Sub Out" from your receiver.
There's also no problem using just one RCA input on a sub that has R/L inputs.
In both cases, you might get a tiny bit of signal power loss. All you have to do is turn up the sub's volume dial a little bit to compensate IF that is the case
No problems and no worries about damage. All you're transmitting through that "subwoofer cable" and the Y-splitter is a low voltage signal. You're not sending any sort of amplifier power - that's built into the sub itself. So there's no problem with splitting the signal to feed two or more subs.
Merry Christmas!
