A mission does not need a location
A mission can be entirely location free, with no point on a map. It opens anywhere, it is solved on the sofa, and it is checked exactly like every other mission. That is what lets a whole route run inside a flat.
You can still use the rooms as stops if you want to. A secret code taped behind a door, a riddle whose answer is hiding in the kitchen, or a photo mission that needs the whole family in one frame.
Three completely different evenings
Chores for the kids, when the house has to get sorted and it may as well be fun. Tidying a room becomes a scored stop, and the competition does the work that asking did not.
A family evening or a night in for two, when everyone is home and nobody is going anywhere. A short route of riddles and photos, with no preparation and nothing bought.