That request seems very normal to me, maybe a little light on all fronts in fact.
On a packer brisket from the package...assuming a 12 to 15 pound packer:
1.5 to 2 pounds lost to trim
35% weight lost during cooking
So, a 14 pound brisket will yield 7-8 pounds of cooked meat. Three servings per pound, you are looking at 20 to 24 servings per raw 14 pound packer.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."