Rights of legal heirs on the property sold by another family member.

I want to purchase agriculture land in Karnataka from a Muslim family. Actually, Muslim person namely Mr.A died in 1965 left behind his wife Mrs.B and two major sons. After demise of Mr.A, his wife Mrs.B got transferred the said land in her name and had Khatha( RTC). But in 1979, another Muslim person namely Mr.C had purchased said land from Mrs.B for a consideration and sale deed registered, land mutation did in 1983 and Khatha ( RTC) stood in the name of Mr.C and Mr.C enjoying the land without any issues up to date. Note 1 : Mrs’s B two sons neither executed gift deed nor relinquishment deed or any deed for their share in the land in favour of her mother while selling the said land by Mr.B to Mr.C. Note 2: Mr.C also not obtained any rectification deed from Mrs’s B sons later. My questions are, 1. Is any legal issue in the sale deed registered in 1979, as major two sons of Mrs.B haven’t signed/not party to the sale deed? 2. If any legal issue, what will be the remedy ?