The TRX is a logical entity, which is carried by a physical board. Your EXxA is carrying 2 TRXs, so if only one TRX is showing some problems, you probably have to replace the EXxA.
(warning: i’m not familiar with your vendor’s equipment, just saying some generalities… I hope it will help)
One “BTS” sector = one cell
You can use also the word “Sector” to refer to the azimuth of the antennas. For example, one sector is facing 100°. In case of multiband or 2G/3G site, several cells could be actually facing this azimuth. One 2G-900 cell, one 2G-1800 cell, and one 3G cell… So here, you have 3 cells on 1 sector.