The sisters in the Sweetwater Mountains on the CA/NV border are triplets. (They are listed as a pair below)
There is a East, South, and North sister in the set.
Thanks, I'm not good in US mountains and this page still needs to be finalized. Thanks for the precision.
If Colorado gets credit for a hat trick for having 3 + 1, it should be noted that the Three Sisters have a Brother as well, and that doesn't count the nearby Bachelor!