Is the grandmother's filing of a fictitious alimony lawsuit—in order to reduce the wife's and children's alimony—considered a sin and false testimony?

It is not permissible for the maternal uncle, the grandmother, or the lawyer to employ a trick to waive certain rights, for this is injustice, and it has been established that injustice will be darknesses on the Day of Resurrection. If the judge rules based on this trick, his ruling is not valid, for he does not make lawful that which is unlawful, nor does he make unlawful that which is lawful. The grandmother's maintenance is obligatory if she has no wealth, by analogy with the maintenance of parents.