Sale of land

there is a land which is owned by 4 peoples including me.....and it is to be sold now....and other three peoples voluntarily dont wanna share in this.....so to bring diz thing in writing whats the procedure......i mean whther any agreement is required to be made or an NOC....if either of the following is to be made then whats the format and procedure.....please suggest i hav never been into such kind of transaction earlier....