Remember that children are a map of their parents in most circumstances and certainly in this case we can see whatever Tapasya became it was because she felt Ichha had snatched her parents love from her. In that case it is Jogi who should have been the one responsible once he realised his daughter was having these feelings to help her out. But since Jogi doesn't know how to be a good father he let Nani poison her more and more and HE HIMSELF ADMITTED THIS! So Jogi is completely responsible for ruining Tapu's life in my opinion.
By that logic, we should blame the parents of every psychotic killer, mass murderer and rapist in my opinion.😉
Pray what do you mean by "let Nani poison"? He did want to send Nani out but was rudely interrupted by his darling Tappa.😆