exemption for appearance in civil suit

I am an absolute owner of land from 20years, the lands are my ancestors property I give to my land to storage of agriculture grassbstorage purpose to some third parties, they are occupied my land and not evicting senior filed a eviction suit against the respondents from my land in 2009 the suit is pending in the court, the defendants stated that they are purchased from my father by way of un registered sale deed, prayed for appearance of my sister's as a party what are the remedies to me, if my sister's are necessary parties in the suit or any other exemption to non appearance of my sister's as a party, any judgements in this regard, please suggest me