How to do it?
Say.. First ask son to move out. Son will move out. The DIL will insist she will stay at the same place that of parent-in-laws.
Give considerable time say a day or two, not more than that.
First give a police complaint against DIL that she is threatening to kill parent-in-laws. At the same time move court. Get NCR number of complaint from police station and attach it to the application while moving to court. Stating that the DIL is a pain in the a s s[threatening to kill parent-in-laws] and that the son has moved out but his wife is still residing with parent-in-laws, get an injunction like above.
Parent-in-laws have every right to live peacefully. Parent-in-laws will get orders as to the effect.
Get rid of the DIL.
Before DIL files a false complaint against PILs, PILs should make the first move, or else be prepared to get behind bars via a false complaint under 498a.
Let your actions be swift. Hire a good vakeel.