Capital gain treatment for legal heirs

Hi Members,

My Friend's Mom sold her Property in the Month of Mar,19 and she passed away in May,19. However she has not invested the capital gain amount in another property nor has she opened a capital gain account. Are the legal heirs bound to pay tax on the capital gain and also if the legal heirs can open up a capital gain account or invest the same in a new property to avail exemption under section 54??? 

Please provide a solution.