What sizes will work for the the 2010+ G37xs sedan? (My stock size is 255/50/18 all around)

I have a extra set of 224/40/18 and 245/40/18, does that work?

 

You should have 225/50, not 255/50 as your stock size.
You need to run all 4 the same or ones that are less than 1% different in diameter front to back. The 225/40 is over 7% smaller than OEM and the 245/40 is over 4%. The difference front to back w/ those new tires you listed is almost 2.5% different.

All those combos are bad. For a winter tire you want narrow for best snow duty, I'd stick w/ 225/50/18s.

 

Narrower tires cut through ice/snow better than the wider ones do. Most functional size with the correct outside diameter would be 225/50-18.