Thanks to the realities of orbital mechanics, the long winter of Sirius B takes up about 25 years of each 50-year orbital cycle. All water in the system is frozen, and in the deepest part of the winter even nitrogen sometimes falls as a liquid from the sky.
Sirius B's eccentric orbit takes it close enough to Sirius A to scorch the planets orbiting it, and then far enough away to freeze it completely. The Long Summer, the ~5 years surrounding the closest approach, causes the second planet Saizok to rise to scalding temperatures. The freezing/heating cycle has eroded the surface of Saizok into a coarse, sandy, flat desert; millions of years of this temperature cycle has broken up any rocks and mountains that might have formed.
Saizok is home to a number of rudimentary life forms which manage to survive for the cold parts of the long year, and burrow underground for the Long Summer, coming out in between to breed. These life forms are studied to improve cryonic technology.
Saizok is the planet around which all four Sirius warp bridges orbit. As such, much of the activity in the Sirius system takes place in the orbit of Saizok.
Before and after the Long Summer, there are two time periods of about 10 years each when temperatures are suitable for life on Saizok.