Don’t fuck with your cousin’s used snow tires. I think your best bet is going to be buying a cheap set of steel wheels in 17 inch size and get snow tires in 225/60/17 inch size. Your Crosstrek requires a wheel bolt pattern of 5x100mm. You can buy these rims off Amazon for $73 each (Vision SW60). I also highly recommend General Altimax Arctic 12 tires.
Tell me you didn’t do your due diligence without telling me you didn’t do your due diligence.