Well I can totally understand Renuka's character. Obviously, she must feel a bit weird and slightly jealous. I wouldn't really call it jealousy, it's more like feeling treated unfair. She was never allowed to do such things and was always restricted, was tied in rules. So now, when she sees her little sister who's just a few years younger than her getting all the things she was never even allowed of imagining, it is a bit annoying to a certain extent. I can totally understand Renuka's character. She's not a bad character, it's just that, because she's been supressed for so long, never allowed to do anything she wants to, so now she's just frustrated watching her little sister and brother doing things she wasn't allowed to do.
If I was in Renuka's place, I think I would react the same way. As far as telling her Mom about Anant and Navya is concerned, I think as an elder sister she would be concerned about what her sister is doing talking to guys when she's clearly not allowed. It's not so much about telling on her or complaining about her, it's more like concern because she doesn't know herself. Navya hasn't told her anything, so it's quite obvious that Renuka will be confused and concerned whether her sister is getting into the wrong company or being used by any chance. So I totally understand if Renuka voices her concern about Anant and Navya getting close because she doesn't know how Anant actually is.