good sister VS evil sister

My sister who is the mother is married with her husband who currently lives in US. Now three (3) years ago we found out that my sister had an illicit affair with another man. We made great efforts to save their marriage. My bayaw pleaded and begged her to stop and end relationship with the man but didnt change her mind. She was very persistent. Came November of 2016 my sister abandoned her 2 kids (6 and 9 yrs old) without any explanation or at least gave us 1 good reason. My younger sister took the mothers responsibility to take care of the kids. Then i resigned from work gave up everything to help. Suddenly a bad news arrived that the mother got pregnant and bore a child with her paramour and living together. So thats the reason why sister left the children. My hatred was raging, shes unforgivable. ngayon po if we come across with the mother tapos tinatawag niya yong mga anak niya pinagbabawalan namin anak niya na makita siya. She reported this to DSWD we explained what happened but still granted the mother to see the kids on Saturdays. I declined this verdict but DSWD told me that i might be sued because mom has rights. Is this right? She abandoned them! (Pasensiya at ang haba ng pasakalye ko)

please help me what to do i dont want any interactions YET between mother and kids. For me Its not YET the right time. May proper time naman hindi po ba? Gusto ko po sana na mag antay muna ang mother till the kid’s minds are fully developed and have understanding towards what happened sa kanilang pamilya. At ayoko ko pong makita ng mga pamangkin ko ang lalaki ng mother nila. Please do advise me.