Hmmm. As far as snow tires I believe it is best to use on all 4. If I had absolutely no choice but to buy only 2 I would follow what Ford says to put the chains on in the owners' manual. The convention I always remember is to put traction devices, ie. snow chains, on the drive wheels. In the C-MAX case the drive wheels are the front, so you want the most traction on the front:
https://www.fleet.ford.com/cmslibs/content/dam/aem_fleet/en_us/fleet/showroom/resources/2017-C-Max-Modifiers-Guide.pdf
https://peerlesschain.com/pages/faqs
Great snow experience shared by our prior moderator:
https://fordcmaxhybridforum.com/topic/805-let-is-snow-let-it-snow-let-it-snowcmax-at-mammoth-lakes-ca/