Dear @Subhu18,
Let me start with a disclaimer: I am clueless about RooFit 
but …
Fitting two Gaussians at the same position but different widths is a very difficult task for any fitter; and it shows in your correlation matrix with off-diagonal elements close to 1 and even one negative diagonal element.
The chi-square of exactly -1 means probably that the underlying optimization algorithm bailed out because some matrix was not positive definite.
How would one distinguish between 2 Gaussians (allowing a fatter tail) and a Hyper-Gaussian shape (see for description )
-Eddy