Let's explore the math, shall we?
The industry standard pitching rate for ales is 75 millions cells/mL/°P
An Activator pack contains, at the very peak of freshness, 100 billion cells. However, because you can't control the transport conditions between manufacture and when it reaches your hands, this number is far from reality.
Assuming a 5 gallon batch of 1.050 wort:
75,000,000 x 19,000 (rounded slightly to make the numbers easier) x 12.5°P =
Roughly 178 billion cells necessary to properly inoculate the wort.
You're underpitching by a fairly significant margin, even more so if you're trying to split a single smackpack between two fermenters.