The yellow discolouration that you see on your teeth are calculus deposits. At this stage it is very difficult to remove them with  brushing alone. You have to visit your nearest dentist to get it cleaned by a procedure called scaling. However you can try xtar toothpaste at night for sometime and see if it makes any difference.

This can't be cleared with paste. Go for professional scaling.

Hello,sir you should visit your nearby dentist for cleaning and polishing ,get your teeth checked as soon as possible and fluorosis is a condition which happens over time and it cannot be instantly reversed ,you can regularly go for cleaning and get a non-flouridated toothpaste advised by the dentist and as per the exposure you can ask him about the correct usage of GC-Mouse for whitening .

Go for scaling and polishing Glodent tooth paste

This is calculus. It is only clear by oral prophylaxis by Dentist. Calculus is made up of bacteria, so harmful to gums and bone. So remove calculus as early as soon possible.