I've raised both niles and savannahs for many years, and animals acquired as adults can be more difficult to work with. You have no control or influence over the years of experience they have had interacting with humans. Whether such past interactions were positive, neutral, or negative is beyond your control. So you have history working against you. Typically, niles are not calm and tolerant animals regardless, and although there are exceptions to the tendency, you should be prepared for an animal that never quite accepts you. You have a better chance (but no guarantees) of getting the savannah to calm down and accept you on some terms, but again, you should not expect it to be as calm and tolerant as it might have been if you had worked with it from hatchling size.
For the nile to calm down and accept you, will require daily - even several times a day - interactions that are non-threatening. Niles also have a tendency to relapse into their old ways if you take a break from interacting with them.
If you are hoping for an animal you can take out and handle and mess around with, then you are probably going to be disappointed with both of these animals. So set realistic goals. That does not mean you cannot set ambitious or hopeful goals, just make sure you have realistic expectations if you do not achieve your higher goals.
There are several ways to improve your interactions with them. First, provide them with suitable hide spots. The ones that serve best for encouraging a monitor to calm down is one where the animal can observe you from its hide spot and with minimal movement completely disappear from sight. My niles had a board where they could sit under it with their heads poking out and with minimal effort pull their head back and be completely hidden. My salvators have the same board now (though my male still gets upset). My timors have logs and wood they can peer out from and watch me (and they do). When they've had their fill or I startle them they pull their head and they're hidden.
Second, position their enclosure so that you never suddenly appear in front of them. Putting the cage near a hallway entrance or right next to a door will probably increase your monitor's defensiveness. One minute he sees nothing and the next minute a giant "predator" is standing near him. Put the cage somewhere so that when you enter the room you are far away. This allows the monitor to see you from a distance and decide how to respond. He can also decide as you approach to respond different and not need to do so on an "emergency" basis.
Third, make sure your interactions are positive. If you're tired or stressed, that is a bad time to work with your monitor. Your tolerance and patience will be lower and your monitor will know you are on edge. They will respond according to how they think you will react, and if they sense tension they will respond accordingly.
Fourth, be consistent. Be predictable. Let your monitor figure out patterns to your behaviors. The better he can predict and know your actions, the more he will trust you.
Finally, be patient. This takes time. Your monitors have a history. You are trying to teach them something different. They learn dangers quickly and safe things slowly. You have to adjust to that.
Good luck.