What is the ruling of the Sharia regarding not repeatedly advising my siblings about prayer and waking them up for it, as commanded by my parents, who become angry if I repeat it? And is it sufficient to wake up adult siblings once for each prayer, along with repeated verbal advice and reminders?

The Prophet, peace and blessings be upon him, commanded children to pray at the age of seven and to be disciplined for it at the age of ten. Therefore, the younger sibling who has not reached the age of ten should not be awakened for Fajr prayer. Rather, it is better to be gentle with him, because prayer is not yet obligatory for him. As for awakening adults for prayer, it is obligatory when there is a fear that its time will expire. This should be done with gentleness and leniency. If there is a fear of harm from repeated admonishment, then there is no blame in leaving them.