Uh ok! I personally worte a .txt file to import the stuff into the RPG Maker MV! You can find it here: "Modern_Interiors" -> "4_RPG_MAKER_MV" -> "IMPORT MANUAL" - There are also some tuorials that explain how to it, here you go! ;)
Uh I got your issue! You need to place the Floors file in the A2 (Ground) slot, the Walls file in the A4(Walls) slot and all the other stuff in a slot from the Tileset B to the Tileset E! Let me know it that one helped ;)