Tiffaney was uncertain if it was the oily, dark feeling, but she did know they were here. Stewards could sense or feel other stewards, but generally only when they employed their power or were in their domain. If that was true either Tiffaney was extra sensitive to it, or they were not holding their strength back at all.
Tiffaney didn't know for certain what her own power was like, but she did restrain herself in some fashion. Descent had given her a few lessons on the unique points of being a steward, but it didn't prepare her to deal with this. The current steward of Dark water was in his early two hundreds and had been steward for decades. His so called first heir was only a kid at this point, and the elder had broken three hundred even if he was retired, he commanded a considerable strength.