Yes
Yes, it can always be divided in 2 triangles. This is because every quadrilateral has 2 diagonals. It is these diagonals that divide the quadrilateral into 2 triangles.
Not true because all quadrilaterals contain 2 triangles
You will either get two triangles, two rectangles, or two irregular quadrilaterals.
Polygon
Not at all. All quadrilaterals can be skewed into parallelograms and so are not strong. They need to have a diagonal brace - effectively making two triangles.
They are called polygons
No. You can have two triangles that are congruent to one another, and two quadrilaterals that are congruent to one another. But the triangle cannot be similar to the quadrilateral!
There are two types of quadrilaterals that are formed when two congruent equilateral triangles are joined. These shapes are rhombus and parallelogram.
Two triangles
You can divide a quadrilateral up into as many triangles as you want, but at least two.
It is a three dimensional figure of some sort.
A trapezoid can be divided into 2 triangles but they are not normally congruent to each other.