Brightness in terms of exposure is always about light per unit area. If you are using both lenses on an APS-C camera the larger size of the image circle projected by the 14mm lens is totally irrelevant.

T-stops are similar to f-stops: the lower the number the brighter the lens. A lens with a transmission of T3.4 is dimmer, by about one stop, than a lens with a transmission of T2.4. Please note the transmission of each lens is measured with the aperture wide open. When stopped down, the transmission will change. For most lenses (but certainly not all), the transmission will be closer to the actual f-number at apertures narrower than the lens' maximum because most manufacturers fudge the number of the widest aperture by rounding it down (brighter) to the nearest 1/3 or 1/2 stop. Some will even round it to the next brightest whole stop!

If you shoot with both lenses on the same camera with the same ISO and shutter time and the apertures of both lenses are left wide open, the 16mm f/2 lens would be one stop brighter than the 14mm f/2.8 lens. This is assuming the slightly wider parts of the field of view for the 14mm lens are equally bright as compared to the field of view shared by both lenses.

If you shoot with both lenses at the same aperture setting, you would expect the two images to be equal in brightness. What minor differences there may be would be due to the accuracy of the aperture diaphragm of each lens.