Answer
(Fatwa: 827/827=M/1430)
In order to straighten the curled hair of beard you can use shampoo or straightener. Beard is the sunnah of the Prophet (صلی اللہ علیہ وسلم) and an emblem of Islam. Every Muslim is required to keep beard to a length enjoined by Shariah. Make your parents understand it wisely and try to send your father in Tableeghi Jama?at. If it is possible, get him connected with any pious sheikh who follows sunnah, in-sha-Allah it will be very much useful.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband