I was a legal assistant for a while, estates was one of my key areas, I've done hundreds of wills, including a couple for estates valued at the time of the will at more than $50M, all in Canada though. So definitely not a lawyer, but I've seen all kinds of estates shit shows.

When you want to leave someone nothing at all, you leave them $1. This way they can't argue they were accidentally forgotten, or a typo missed them, that kind of thing.

Sure, fighting estates cases is pricey as fuck. And you can always litigate. But if OP's grandpa is as shrewd a business man as it sounds, I'm sure his will is pretty tight. And if that's the case, whatever additional legal fees OP would accrue through litigation would hopefully be awarded in costs. And if the size of the estate is as big as OP seems to suggest, Gramps should set up a Trust and be done with it. Insofar as the bulk of the wealth is held in the trust, if none of the other family members are parties to the Trust they can't even litigate (or at least, in my neck of the woods, you would waste money having your lawyer write letters requesting to see the Trust documentation, only to be told "nope" several times over).

All that said, OP's Gramps definitely has lawyers better than our internet speculation.

OP - ask your Grandpa what kind of Enduring Power of Attorney, or Advanced Health Care Directive he has in place. Whoever is named in those documents would gain access and control of his estate if he were to become ill and unable to operate his own estate. I had a tragic case where a woman had left her estate to be evenly distributed amongst her grandchildren (all adults aged 30+) but had named her daughter her power of attorney. This lady developed dimentia late in life and her daughter liquidated all the assets and funnelled all the money into her own accounts, and then spent it. (Over simplification of the case, but this was essentially the issue.) While this was a mismanagement of the estate, the grandkids need to litigate to recoup funds already gone - they will win the case, but will never see that money.

So OP, be sure you know who gains access to what assets in the case Gramps becomes incapacitated but not deceased. But again, I'm guessing Gramps knows all this.