Capital gain

My query is regarding capital gain on sale of residential house which is name of mother and son. After selling the same son has invested the same in another property which is in the name of his own and his wife jointly. How to compute capital gain. I think sale consideration and cost of acq will be devided equally between son and mother and son can take exemption u/s. 54 for new house property. In case of mother she will not get exemption. Whether she can claim benefit u/s. 80C against this income?