Your husband is being unfair to his brother.
And you're probably the only one who can get him to see that.
"I'd like xyz if no one else does."
Someone else DID.
Also... Not everyone immediately has "stuff" on their mind. It may have been a piece BIL had wanted for years, but the split second your husband announced he wanted xyz should not be the ONLY time its "okay" for BIL to say so. People process differently. Just because your husband thinks faster about what of the estate he wants, doesn't mean it's first come first served, kwim?
BIL (and their parents, and the aunts/uncles/cousins) are JUST as 'deserving' of gramma's estate, as your husband.
But grieving, he may not see that.
He may ALSO not see that taking things pre division of assets in the will is often considered to be 'looting'. My family has no problem with that (we put our names on favorite things in tape or pencil, decades before people even get sick, much less die. But in many families, laying claim to things before the will is read and estate divided, considered beyond rude. So there may be many people who would in fact like xyz, but would never say so until she passes (or are caught flat footed when someone starts "looting", and come along later saying "Now wait just a minute..."
Which sounds like that's EXACTLY what's happening... Since people are starting to call you.
Point being... Your husband is definitely being unfair to his brother, but may also be walking on thin ice with the rest of his family. And is clueless about how he's hurting others.
Which means you would be INVALUABLE to him, and to his family, by playing the peacemaker that only a beloved spouse can.