Answer
(Fatwa: 492/298/H=1433)
Keep on taking care of your father and do not say anything him about tablighi jamah. However, with the advice of local tablighi jamah people request to some such people who have already spent their time in tablighi jamah that they should come to your father and talk to him a little about tablighi along with business and home related talking with wisdom and insight. If any outside jamah comes then the local people should get your father meet them and you should not be there that time. Recite the last ruku of 13 para [واذ قال ابراھیم رَبِّ اجْعَلْ هَـذَا الْبَلَدَ آمِناً ……… رَبَّنَا اغْفِرْ لِي وَلِوَالِدَيَّ وَلِلْمُؤْمِنِينَ يَوْمَ يَقُومُ الْحِسَابُ سوره إبراهيم] before sleeping in the night or in tahajjud after performing tahajjud salah and make dua for your father. May Almighty Allah bestow him correct understanding and sense!
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband