@Izan is right. When using a single 1.0 ohm coil your overall resistance will be 1.0 ohm.
Using
two 1.0 ohm coils your overall resistance is "halved";
0.5 ohm total resistance. The lower resistance will produce a warmer vape, more vapor, at the expense of draining your batteries faster.
What batteries are you using by the way? Brand, model, and amp rating?