Son sold us his father property, daughter demanding money

Too much of water flown, they were sleeping  like rip van winkle;  how was the sale deed registered then, they can file a suit but chances are rare nearing to zero ; however they have share in the property but they should ask that from their brothers. So tell them to ask their belated demand from their brothers as you have paid the value and tell them to file suit against brothers and you will testify that you paid full value f property to them.

What is they're rigid about there decision about lodging case against property rather there own siblings?

Will that case any harm to us? Can they legally do that? If so, can we win?

They're asking for 1.5lk, is it worth to just give amount and get thr sign? Or can we fight case?

Well they can file a suit since they are shareholders and not been witnessed in the sale deed, it is better just to pay them the meager amount and get rid of yourself. You should let them sign the receipt of money clearly mentioning in consideration of their sale amount in the specified property ; besides you should let them sign a deed of relinquishment thereby relinquishing their share in to you against the amount of money.

But if you want to contest the  case they will certainly get defeated on many grounds but that is time and money consuming for them too as they cannot keep fueling the case. 

You allow them to file the suit by impleading their male siblings and the remaining legal heirs along with the other buyers,  if some buyers are reported to have died then the legal heirs of the deceased buyers  seeking partition and allotment of their share. 

By the time the suit comes for trial it will be two years or more. 

Once the trial is conducted properly,  you can challenge the case properly and refuse to accede to their demands.

The court will then decide the case on merits