I am now using PYROOT to integrate ROOT and Python. I was looking to this thread on how to write the function for the minimizer How to pass fcn func defined on python side to ROOT.Fitter?
I found the TMinuit class reference https://root.cern.ch/doc/master/classTMinuit.html
I have found also this tutorial on how to use minuit in ROOT http://superk.physics.sunysb.edu/~mcgrew/phy310/lectures/phy310-lecture-11-2007.pdf
I am struggling into integrating all this information together and I cannot find a tutorial about minos that you mention, it would be useful if you could point me to relevant resources on how to minimize chi2 and finding errors.