it is obvious as long as SINAL is around, Rohit can't get close to Vira.
But besides that Rohit wanted to take revenge on SINAL for long time, especially Kunal. SINAL are responsible for Vira marriage. Even during rape case, Rohit said the reason he was helping Witcha was to take revenge on SINAL.
Right now he is more interested in harming Kunal then Siddhi. Besides even he knows that SINAL are kind of inseparable - one who can't live without each other. So really all he needs to do is get one in real trouble and other would simply break due to pain of losing other. As Kunal had said if anything happens to Siddhi; his life is finished. Siddhi also has no life if there is no Kunal.
As per him being alive; it sure is a problem. But in his mind (not entirely wrong) if one of SINAL goes to jail, either one won't survive due to separation. Or he can also go live in other city. But how will he get Raveena? May be in his mind he can show Raveena how powerful he is😕
It's same as Witcha thinks if Siddhi is not around; Kunal will come to her🤢
In short both Thakral kids are out of their mind to think this way, may be runs in family😆