Legal Question in Wills and Trusts in California

Yes, they can contest the Will as potential beneficiaries but are not likely to have any chance unless she had adopted them. If she did adopt them they wold have to show she forgot to include them, but it is very common that a spouse does not pass anything onto the other spouse's children. You need to see an attorney with all the details so that a letter can be written to them explaining what the law is and why, if the situation, they have no chance of winning.

Mr. Shers is right if your grandmother's husband's estate was probated. That was his heirs chance to assert their claims. If his estate was never probated, which is unfortunately all too common when the first of an elderly couple who held everything jointly dies, then they may have a shot.