All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is not obligatory for a son or daughter to obey their parents in everything that they request of them. Rather, obedience is only obligatory in matters which are to their interest and which do not involve harm to the child, as the jurists have stated. Please refer to Fatwa 131695.
Therefore, if it is of no benefit to your parents to ask you about the amount of the assistance, then they should do so, and you are not obligated to inform them. However, you should try to please them and avoid anything that angers them.
If doing so is of some benefit to them, but informing them would cause you harm, then you are also not obligated to inform them.
Allaah Knows best.