The Biskit Mansion is a home owned by Fisher Biskit, where he and his twin daughters Whittany and Brittany, and butler Francois LeGrande live.
The main floor is large, with a portrait gallery in the main hall, some of which feature the twins riding unicorns. A staircase leads to the second floor, with several hallways leading to many rooms. One of which is Whittany's bathroom, in which Fisher bought a golden doorknob online to adorn it with.
In Winter Wonder Wha...? The mansion is also shown to have a large sitting room with a fireplace, where Fisher sits and reads the paper.
The twins have a room, which may be a bedroom. Where they use laptops and keep an entire armoire full of laptops.
Francois we can assume has a living quarters, as he is a full-time butler, as well as bedrooms for Fisher and the Twins. Shown in the Littlest Pet Shop Original Short So Like Bored, it is confirmed that Brittany and Whittany share a bedroom, though it could be implied that their bedroom may be in close proximity to Whittany's bathroom, due to convience and the twins history of being extremely lazy.
They have a large dining room, which Roger played board games with them in Grounded.