Can the magnitude of the sum of two vectors ever be less than the magnitude of either of the vectors?

Gravity is a vector, because it is a form of acceleration (which we know by definition is a vector). Vectors hold more 'information' than scalars, because vectors are, put simply, a scalar + a direction. To help you figure out these types of questions in the future, all you have to do is figure out whether direction is an important aspect of the value in question.

The question asks whether it is possible to add two 'equal' vectors, and end up with a vector whose magnitude is equal to the magnitudes of both the vectors. The wording is not very clear: either the two vectors are themselves equal, or their magnitudes are equal.

If you add two vectors with equal magnitude, and the magnitude of the resultant vector is equal to the magnitude of both vectors, then the three vectors obviously form an equilateral triangle. As @almagest said, this means that the difference between the angles of the two vectors is $120$ degrees.

If the vectors are equal, then their sum will necessarily have a larger magnitude than either of them unless the vector is zero.