Harrasement by wife

My brother got married in 2013 with oc women.we bebelongs to schedule caste .they are worked as engineers.It is a love marriage.she asked my brother to change your caste before marriage.But he did not agree that.After marriage she is normal to husband' only one year.she did not give any respect to my relatives.In 2015 one male child was borned.After then she wants change the caste of child.My brother did not agree.Then she harrasement begins.She blackmail s my brother by using child .My brother take more care to that child than mother.She went to their parent's house in november2016. She did not come back till today.She went to tirupathi with his child ,and her sister ,brother in law and her parent without information to her husband. She also went to Basara for akshrabhyasam to their parents,sister ,brother in law without any information to husband.She also joined in school also.She wants to live her child with their caste relitives.she uses my brother as labourShe did not give child to my brother..she wants only my brother without any relations to schedule caste relitive.ßShe did. Not give any respect to husband. Then what we are doing in that case.Her brother in law harrases .Does my brother ask divorce from her.Do we file sc ,st attracitty case against her,and her relatives.My brother worried about his child.Please sir give correct suggestion to get my brothers child.How to proceed about it?.