In Twinmotion will change the material for all objects that have the same surface in AC. It does not matter what type they are in AC if they have the same surface then when you edit it in TM then all will change. Solution is either assign different surfaces in AC to the objects the objects that will have different materials in TW. Option to try is to export 2 different files from AC one structure without furniture and the other with the inverse selected. Importing both into TM might let you assign different materials to the same surface.
Also while modeling in AC different types of objects should not have the same surface i.e. a Slab surface might be the same for a Wall or Roof but it shouldn't be applied to a table, sofa or curtain.
AIA NCARBAC26 US/INT -> AC08
Macbook Pro M1 Max 64GB ram, OS X 10.XX latest
Learning: VW, RVT
Teaching & Using: AC, Rhino, ACAD, RVT, SU, AI, PS, InD, TM, C4D, ATL