Is an income of MYR 10,500 per month in Kuala Lumpur sufficient for a family of four?

With that amount of income, you'll fall under the middle income group. Most households do not even have a combined family income of RM10,500. You can lead a ordinary but comfortable lifestyle and can afford some luxuries once a while. Pursuing educaton in an international school is not cheap. In the end, you might not have as much monthly savings as you desired.