Father Right To Visit His Kids

Dear Sir, Meri sister k two bache hai... one is 4 yr old son and one is 8 yr old girl. main apni maa k ghar last 3 and half year se apne pati se alag rah rahi hu... ab unhone ghar basaane ka case file kiya hua hai.... kya wo ab father rights to visit kids ka case file kar sakte hai......... and if yes.... to mere paas kya solution hai ki main unko apne bacho se milne na de saku... kyo ki last 3 and half yr se main hi sb kuch dekh rahi hu ... please give valuable suggestions... thanx