The best remedy available when a family member refuses to partition joint family property is to file a suit for partition before the Court of jurisdiction where the property is situated
Yes, a co owner may sell property without partition of the same but if you are aggrieved by such sale you can challange the same in competent court of law and implead the purchaser as a party too.
You can take stay on sale or construction of the disputed property by moving an appropriate plaint along with the application for stay under order 39 rule 1 and 2 of the code of civil procedure
No registration and mutation alone do not prove anything with regard to owner ship. The law says possession and 99 points ownership. Possession is generally a good ground to claim ownership but the same should also be clubbed with documents showing ownership
For encroachment or illegal possession one can file suit for permanent and mandatory injunction and along with that apply for appointment of local commissioner from Court for ascertaining the factual position
For general information or appointment requests, feel free to contact Siddhik Law Chambers.