It is said that one accumulates sin if Sandhyavandanam is not performed daily. Does this apply to Tiruvaradhanam as well? Will one accumulate sin even if Tiruvaradhanam is not performed by an individual?

There is a small difference between Tiruvaradhanam and Sandhyavandanam.
Sandhyavandanam is to be performed by every male member of the house. For example, if one person in the household performs Tiruvaradhanam, that is sufficient. Others can simply acknowledge it and receive the Perumal Theertha (holy water/prasad). However, if no one in the household performs Tiruvaradhanam, and if Perumal is present in the household and Tiruvaradhanam is not performed, then that is indeed a fault.