Harassing father in law and mother in law

Hello Sir, Mother in law (50yrs) father in law (55yrs) and they have daughter (26yrs married) younger son (27yrs,unmarried) their elder son 28yrs got married in the month of march 2015,the dowry which was given by girls family was used for his marriage purpose only.This all things were happened in der presence v have taken d dowry n cleared all the money which v borrowed for marriage purpose.After one month their daughter got married and not even a single penny was left out from daughter in laws dowry to use for their daughters marriage.Daughters marriage was done by borrowing some money from others.After this the son was not willing to go for a job if he goes he wont give a single rupee to his parents.Meanwhile the daughter in law was creating some scenes with in law so she was sent to stay with their son.She nver says him to go n do job.They both were depending on in laws .Meanwhile father in law one owned property house was solded out and cleared all the financial problems.For 18 months they both dependent on in laws.At last in laws loosed their patience and told their son to go for work and earn yourself and stay happily.Meanwhile the son n daughter in law were not able to to withstand and dey came back .Dey all stayed in a rented house together.After two months ,daughter in law became pregnant and son dropped her in her parents house.And he went back to search job.For 20 days he went to work and meanwhile he stopped talking to his parents.From der he went to daughter in laws house to stay along with her parents.Meanwhile she started spreading news to all the relatives of in laws that she will file a case against her in laws to give her dowry back and son and daughter in law contacted der daughter who was married saying that the cash or dowry which was given to you and husband is our cash .During their marriage the son has given his gold chain to groom (daughters husband) on his own interest .That chain was given by daughter in laws family to their son.Now they started demanding to return their chain back and money which was given to their daughter . So now how to solve this problem