mukesh 01 June 2018
R.Ramachandran (Advocate) 01 June 2018
Have you all spoken to your mother about this? If not why not?
Apart from that, please remember, if the property is in your mother's name and if she sells it, none of you (including your sister who you say has taken the document etc. etc.) have any right to object to your mother's action.
In the meanwhile, if you all talk to her and convince her not to sell the property and if she accepts your request, that will be a different matter.
Otherwise, your mother has every right to do whatever that she wishes to do with the property.
mukesh 01 June 2018