SHARES IN SISTERS NAME DURING PRE MARRIAGE AND POST MARRIAGE

Hello All , 
My father maintained my sisters Income Tax file with CA before marriage  , He had invested around 1 LAKH in multiple scrips, now after marriage gave the file to in laws to continue for taxation purposes , now with time my father passed away and shares are valued now at 5 Lakhs ,  in laws keeps telling me to sell those shares and release cash in file , i have no idea what to say them , in this case What should i do , they don't know anything about share market ...and i don't know why the want to increase cash in hand in files by selling shares .
1) Can i open trading account in sisters name and sell those shares , either they can or i can they will get credit amount of 5L in books recorded and i can get 5L as cash from her In-laws 
2 ) Not clear whether these shares were gifted by my father or not to INLAWS as per my mother claims that once in laws gives 5L as cash to us , we can sell those shares and give credit of 5 L as White in her files 
So please help me with these 2 questions ..