Hi! Sorry for the late reply. If I understand you correctly, you have problems with the walls of the A4-Tilesets?
The centers of the tiles repeat, thus forming the wall to connect the corners. RPG Maker automatically repeats this part of A4-tileset when they are placed in the A4 slot in the Tileset-Options. For other Engines you may adjust the graphic.

Width of the Corners: 24px. Width of the Middle: 48px.

Same goes with the height of the Wall. The "roof" works similar.
I hope this helps. If not—or if I misunderstood the problem—please let me know.

