Centre-back Sanchez has been linked with a move to Barcelona after impressing in Ajax's run to the UEFA Europa League final last season.
Younes, meanwhile, is reportedly a target for a number of Bundesliga clubs, while striker Dolberg has been tipped for a move to the Premier League or Serie A after scoring 23 times in all competitions last term.
Overmars, however, has no intention of allowing Sanchez to leave on the cheap and has ruled out the prospect of selling the attacking duo, who he hopes will learn from experienced forward Klaas-Jan Huntelaar in 2017-18.
"Kasper Dolberg and Amin Younes are not for sale," he told De Telegraaf.
"Klaas-Jan Huntelaar and Dolberg are a top tandem of master and student."
On Sanchez, who has also been linked with Real Madrid and Inter, Overmars said: "For less than €40m, he's not going anywhere."