This is confusing as there is no way they would know if you were a carrier just from the sweat test. Only people with CF have the heavily altered chloride levels, there is no alteration in carriers. You can have borderline tests even if you don't have CF, or aren't carriers, but not have high enough chloride levels like someone with CF would have.
I would suggest getting a blood test to genetic test your family, this will be the only way to diagnose if any of you are carriers, or god forbid, have CF.
Hope everything turns out to be fine
All the best