What your relatives say to you is meaningless. You should not make any decisions without actual facts and information.
Contact the executor and ask for an accounting of the estate and a copy of the will.
Review this with legal counsel if you have any questions whatsoever about what something means or if you see something that is not easily explained.
Spoken with the wisdom of someone who has been through some things. I agree.
You don't know them that well, per your post, so I'd be hesitant to sign off on anything. Especially not under any kind of pressure. Evaluate the situation first: get the facts.
Realize, too, that it's really easy for people to get greedy and for people to hide things: they may not be telling you that there's X stocks, or X gold, or whatever it is, because they're hoping you'll sign off and then they'll own it all. It's sad, and I hope that's wrong, but it's frankly
very odd that they're asking you to disinherit yourself over things that weren't your fault to begin with. It smells like greed. (Or perhaps desperation, since they planned on another outcome only to now realize that's not what's happening.) Either way, it's not necessarily what's right.
With that said, I would value people and relationships over money. But you also don't want to be a sucker for someone else's greed/desperation, which is just more enabling behavior, this time, on your part. It's tough to walk that line, and you can't do it here without the facts.
I will say this: the burden is on whoever wants to change the will (because that's what this is: distributing
not according to the will) to prove the absolute necessity of that, how it wasn't factored in already, and so on. Even shares is a pretty easy way to keep things fair, and all the more so here.
I can't say which way you should ultimately lean or whether, like some suggest, a compromise is in order, because we just don't have all the facts. Sounds like you don't yet either. With that said, I would be very skeptical in general of folks pulling out things from the past that you aren't that familiar with, don't really know about, or aren't really sure about. If it's not enough to prove it in court, then why are they wanting you to just accept it as true, to your own detriment? I'd be very skeptical in general. In other words, my bias would be strongly against changes, absent some very impressive proof and so on. Keep in mind: you're only hearing one side of a story, it sounds like, and the folks who really could have filled in the other side (grandparents, your mother) are all gone. (Proverbs 18:17: "The one who states his case first seems right, until the other comes and examines him.")
Best wishes to you on figuring it out: it sounds like a headache either way: you either forfeit a good chunk of funds or harm relationships, and, either way, it's hard not to be skeptical that those relationships are worth much anyway due to the eagerness to have you forfeit large sums of money for them. All around sad, especially after a loss; you have my condolences.