Counter sue

There was a civil case against us on property issue. But sale was held on valid grounds and we have clear title of property. The party was sellers children who fought amongst the siblings for property share. As one of purchasers of property, a court summons was issued to us to which we didn't attend. They did try this suit 5 years back to which we were exparte but judgement was against them and we won as one of defendant with no costs as decreed by court. Again they have instituted civil suit and my mom is one of defendant unnecessarily. I had enough of their quarreling amongst themselves with my mom being dragged now. Can i countersue on the basis of medical grounds i.e. anxiety or stress related with doctor certificate of my mom and on basis of fall in market value of our property due to invalid injunction placed on property and on basis of previous judgement? How much amount can i sue them for?