I would support both of them.
During Param's fiasco, there was nothing hidden from Ishita's side. From the beginning of the story, Raman knew Ishita speaks truth like the Coffee wala incident before marriage where they shared the same auto to reach home. During that time, she said to Prateek that she was with Raman. Such similar incidents make a person trustworthy. Also, her care,affection etc towards his family made him support her,
Coming to Ishu's behaviour, it is not that she does not trust Raman. But her trust on Raman is very weak i would say. She tries to believe Raman, but the situations make her to lose that trust which she built on Raman. During that stem cell scenario, both spoke and decided that they share everything about their children things with each other and both will be support for each other. She had built trust on him, but what happened , Raman hid Adi who was culprit in amma's accident track. Here, her trust is broken, Coming to Mihir's sister fiasco, Raman could have disclosed Shagun is mihir's sister and closed it and could have asked her not to create any issues further. She would have done it, Didn't she do the same with Adi's case when she came to know about it before Raman disclosed it , If , she had thought, she could have got punishment to adi but she was silent. Instead of that, Raman shouted on her, Also, when she had asked Raman about Sanjana, Raman could have immediately said no,instead he thought for few seconds and then said no, likewise, there are several incidents where ishita would build her trust on Raman stronger and the next moment, it is broken.
Raman's trust was grown stronger day by day as there were no such incidents which is hidden by ishita and Ishita's trust was weakening day by day as there are lots of incidents which is hidden by Raman,
I hope,atleast in future, both trust each other and share everything.