sheriff5.yft, sheriff5.ytd, and sheriff5_hi.yft go here:
Grand Theft Auto V\update\x64\dlcpacks\mpchristmas2\dlc.rpf\x64\levels\gta5\vehicles\xmas2vehicles.rpf

carvariations.meta goes here:
Grand Theft Auto V\update\x64\dlcpacks\mpchristmas2\dlc.rpf\common\data

vehicles.meta goes here:
Grand Theft Auto V\update\x64\dlcpacks\mpchristmas2\dlc.rpf\common\data\levels\gta5