بسم الله الرحمن الرحيم
According to Shariah, as long as your mother is alive she is sole owner of the flats owned by her and if she distributes it among her children and gives the share of each one into his and her complete possession then she can do so. She can divide the flat into eight shares and give each son 2-2 shares and each daughter 1-1 share. Rather, instead of eight shares, it can be divided into five shares as well and in this case each son and daughter will get equal share, this is the best option. Your mother is advised to do whatever she wishes with mutual consent of all children and by taking everyone in complete trust.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.