Title declaration & possesion requires

In the year 2003, a plot of 30 * 50 was purchased through a notary in the name of the mother & in 2009/10, the lower floor was built with the financial help of the whole family ( Parents & All three brothers A'B'C' respectively ) , Post construction ' A'was living in 20*50 area with parents and his wife & children and still is, in the remaining 10*50 area 'B' was in residence with his wife & children And this part is still in the possession of B, rest remain ' C'who lived on rent in another city because of his job & who is still living on rent in another city with his wife and children, Apart three brothers they have three sisters also in family , all of them are married. Father passed away in 2016 and in year 2017 'C'got married and according to his mother's oral verdict , 'C' constructed two rooms on the terrace by his own money for him unfortunately Mother died in the very next month after her death and in absence of C , B capture the rooms of C and kicked him out of house . Whenever C goes and ask for his rooms, B is creating dispute & threatens him. The whole first floor and 10*50 of ground floor in in possession of B ...the plot is still in the name of the mother, whose registration has not yet been done nor the map was passed by Nagar palika . Pls suggest step by step How can I & my sister's can claim the property .
Note : This is a case of Muslim family &' B' ( middle one ) is creating dispute not 'A' ( eldest one