You may find it useful to take a look at More Isometric Areas.

These diagrams might help you to work out the areas of the tilted triangles.

The top diagrams show how drawing a non-tilted triangle around the tilted triangle could help you to find the area of the tilted triangle.

Area of tilted triangle = Area of blue triangle - Area of 3 green triangles

This diagram show some lines that can be drawn inside the tilted triangle:

Area of tilted triangle = Area of pink triangle + Area of 3 blue triangles