The testator of a Will can very well subsequently transfer some of the properties by settlement even if there was a registered Will made by her, without cancelling the Will. If the Will comes to force, then it can be executed for the remaining properties as on the date of death.
If you suspect the transfer of certain properties by settlement was done fraudulently then you can challenge the same with the support of substantial documentary evidence to prove the fraudulent activities.
As a matter of fact your grandmother chose your grandfather as first beneficiary, though it was a life interest alone.
It is not known what suit has been filed and why you people did not take any action to restrain your grandfather from alienating the other properties during the pendency of this litigation.
You should have filed an injunction petition simultaneously.
Further the stage of the case as well as the pleadings from your side to protect your interests are also not known hence any advise rendered now in this regard may be a misguidance, therefore you may be in touch with your own lawyer on all such further issues.