Assuming that the model is adequate and appropriate, then to answer your second question:
Which frequency out of those five is right?
All of those modes and frequencies are possible in the structure. Usually the frequencies are provided in increasing order (i.e. the numerical smallest is presented first etc).
The frequency that is usually more important, are those that are closest to the excitation frequency. This is because eigen frequencies in the structure close to excitation frequency can cause resonance.
a note on "Right and wrong"
regarding the first question:
How can we make sure that our analysis is right?
I should point out that all the frequencies are "right" and at the same time "wrong".
- right because those are the eigenfrequencies that the SOLIDWORKS model has calculated numerically
- wrong because the Solidworks model is an approximation of the structure and so you can't really rely on them.