They may be pest snails, or they may be beneficial snails ...depends upon your view. I can't tell, yet, what type it is, but the common "pest" snails are pond/bladder snails or ramshorns. Your nerites won't reproduce so, the question is: will three nerites keep your aquarium clean and help with algae control? If the answer is "yes", then any other snails are superfluous. If the nerites can't keep up with the cleaning, then other snails will help. This is a function of how much you feed them, directly or indirectly. If the "pest" snails multiply rapidly, that means that you are feeding too much and/or you have other things dying in your tank and becoming food and may not be cleaning well enough. The population will die off if it does not have sufficient food. In any case, they generally act as a good clean-up crew and, if their population is under control, can be a good indicator that you are feeding properly and cleaning well. I have intentionally added red ramshorns to my tank.
Getting rid of "pest" snails is extremely difficult on a short term basis and, no matter what you try, you will have to remove the nerites to a different tank and nurture them until you determine that the pests are gone for good (their eggs are incredibly hardy and long-lasting). The food sources can be reduced enough, with meticulous cleaning and food control, that they will starve and gradually die as new ones hatch before they can lay eggs, but this can take a couple of months. You can treat tanks with chemicals, such as copper, to kill them, but this can harm all other life in the tank if not done carefully. There are tricks, such as leaving food in traps and removing them when they fill with snails, but this just reduces the current population. However, combining this with starvation in the rest of the tank may speed the process a little.