Praise be to Allah.
It is not permissible to delay praying Salaat al-Ishaa or any of the other prayers. Whoever prays them late, not at the proper time, is a sinner who is guilty of a major sin, because Allaah says (interpretation of the meaning):
Verily, Al-Salaah (the prayer) is enjoined on the believers at fixed hours. [al-Nisaa 4:103]
Guard strictly (five obligatory) al-Salawaat (the prayers), especially the middle prayer (i.e., the best prayer Asr). And stand before Allaah with obedience [al-Baqarah 2:238]
You have to pray on time, without delaying it, and advise your parents with regard to the issue of prayer times. Tell them that they have to let you stay awake so that you can pray, and try to help yourself by taking a nap during the day, which will make it easier for you to stay up for the prayer. The Prophet (peace and blessings of Allaah be upon him) forbade sleeping before Ishaa lest a person miss the prayer. If your parents force you to sleep, do not obey them, even if that means pretending to be asleep until the time comes and you pray. May Allaah bless you and help you to adhere firmly to the Straight Path.