Hey Brother Smoker-
It's my personal preference, but I don't like the texture of reheated brisket, and especially frozen, thawed and reheated. It can get mealy/grainy, and worst of all, a drier, chewy texture (especially the flat). The drier texture can be compensated for to a small degree by bathing it in broth or Au Jus when reheating, but that only goes so far, and for best results it needs to be thin sliced which in a way gives a false sense of tenderness.
By cutting the brisket in half (across, side to side), you will have one piece that is mostly the flat muscle and another which is mostly the point muscle, as they taper towards the center of the length of the packer, with a fat layer in between these muscles. If cut into thirds, you would still have one with both muscles (from the center), one with mostly the point and one with mostly the flat. The point being more of tubular muscle construction with much more marbling of fat, while the flat is a fibrous muscle construction with far less fat content, the point is more forgiving if mistreated during cooking, or in extreme situations of reheating. The flat, in contrast to the point, can become a dry and leathery texture if mistreated.
That said, if I were to cook it whole and freeze the leftovers, I would eat the flat and freeze the point, as the point should be the best candidate for freeze and reheat. BTW, I typically use the entire point for burnt ends (not just the heals of the brisket after slicing it up like BBQ joints do)...they are a favorite here, and I usually catch a ton of flack for not not making burnt ends when I smoke a whole packer...yes, we love burnt ends.
I'm in the same boat as you, with just 3 mouths to feed now, unless we invite someone to dinner. If it were me, I'd cut it in thirds and smoke those smaller sections in a smaller cooker...just because I like it fresh better than reheated. We have a hard time using up our leftovers if refrigerated, and freezing does break-down meat fibers even more...it's that texture and the lack of a consistent, effective method to control moisture loss that just turns me away. I'd rather toss something on the grill for quick cook than eat leftover meats...I guess I've gotten finicky, or maybe I've just given up on the search for an acceptable reheating method which gives acceptable results...
Hope this helps you in deciding what is best for YOU...doesn't matter what I like best, but you can probably relate to much of this and weigh you options. I'm probably forgetting a few things, so this is by no means viewing the picture from every angle.
Have an enjoyable smoke and a GREAT brisket dinner!!!
Eric