If all is booked on one ticket they will stay in the airside part of the airport.
They should be aware not to follow the most of the fellow passengers but follow the signs to transfers or to the letter of the gate they leave from in Schiphol.
As you have seen there are maps available and gates are assigned pretty early, but that makes the risk on a gate change bigger so looking at the screen with the gate information is essential.
Coming from Warsaw they will exit the Schengen zone and will go through exit passport control in Schiphol. I have never transitted there but I believe that there is a dedicated border control area for transit passengers.
If they accidentally exit the secure area or want to go out of the airport they can join the passengers who will start from the airport and go through passport control and security, staff in Amsterdam is used to many who do not speak the languages they know.
I think the suggested ask for assistance is a good plan but if they do not want that (my parents were very stubborn about that) they should be fine.
If they get stuck, go to any uniformed person, show boarding card and look with a question in the eyes, most will understand and at least point in the right direction.