If brother in-law is sent a sealed copy of the will is he to open it in front of all the sibilings of the parent that passed or can he just open it in front of just one of the siblings and go through it all then just read some of the papers to the rest of the sibilings?
Often a will was done decades prior and written when there were oodles more assets so when they actually die the estate is quite small or nonexistent. All those thinking that there was going to be a windfall of cash find that instead they are 1 estates asset distribution away from being able to buy a used car at best. I was executor an aunt with this situation.... lots of high hopes by folks for $$$ but the reality was that there was lots of messy debt and property with bad chains of ownership which is tedious and costly to unspool.
Once the testator dies and the will comes into effect, it is then a public document. There should be no reason for the executor not to make it available for everyone who wants to to see it; but if that's inconvenient to him for some reason he is free to tell you to look it up yourselves.
It sounds as if you suspect your BIL of "editing" the will? Legally, he can't do that. An executor is required to carry out the instructions in the will, period, whether or not any beneficiaries are aware of what they are.
Would you like to say a little more about what is worrying you?