WAIVER OF RIGHTS WITH GENERAL RENUNCIATION

Good evening Atty .  I would like to ask your advice regarding  an inherited  property. Before my  grandmother died , the remaining properties were  already transferred  and titled under  the names of  her children , not individually but as co-owners  and it was agreed  among them that certain parcels of land will be shared by particular co-owners (i.e. parcel 1 should be shared by co-owner 1 and 2 and parcel 2 will go to   co-owner 3&4 ). My problem is that my mother who shares a parcel with one of her siblings already passed away more than 10 years ago. The parcel is still titled under all 4 of them. Can we just execute a waiver of rights and general renunciation to allow me to process titling of my mothers share to us , her children ? What other steps should I undertake ? Thank you very much .