Will the supplication of the siblings against their father, due to their belief that he is stealing from them, even though his share is greater than theirs, be answered, and will envy affect the questioner's deeds?

It is not permissible to supplicate against anyone unjustly, and whoever does so is an oppressor. Allah does not answer his supplication if he supplicates for sin or for severing kinship ties. The best way to ward off envy is to consistently recite the morning and evening adhkar, especially reading Al-Ikhlas and Al-Mu'awwidhatayn three times, for they suffice against everything. The Prophet, peace and blessings of Allah be upon him, used to seek refuge with them and abandoned all else. There is no need to fear the failure of matters, for everything is in Allah's hands. Whoever fears Allah and trusts in Him, He will suffice him in every matter. Allah Almighty said: "And whoever fears Allah - He will make for him a way out. (2) And will provide for him from where he does not expect. And whoever relies upon Allah - then He is sufficient for him."