Dear Mr. Abdul Rahman;
Your deceased sister's share in proportion was allotted to another sister as per court order (?), right? Therefore that becomes her property and upon her demise, her property shall devolve on her legal heirs which is natural and legal, do you have any doubt in it?
If the property left behind your sister is not given to her legal heirs, is it not an illegal act?, under the situation where is the question of her legal heirs trying to grab the property?, they would like to inherit their mother's property legally, this cannot be said as grabbing. If they try to grasp more than their entitlement , it can be considered as grabbing and illegal.
You may issue legal notice to them if they try grab your property to not to interfere in your possession and enjoyment of your property and subsequently you may file a mandatory injunction suit against them on the same lines.