Yeah cooking for two can seem to be a issue but it's really not. We are empty nesters here but that doesn't stop us. I still smoke 11-12 lb briskets. We eat our fill that evening, then during clean up we portion out the remaining into dinners for two, place them in foodsaver bags, suck out the air and into the freezer. Thawed and warmed they are still great!
Regarding toughness and brisket: (remember I'm coming from using whole packers, point and flat still attached...) its all about getting the brisket to the color you like, then we double wrap tight in foil and put it right back on. This helps power through the stall AND preserves the moisture. It's done when it done - i.e. when a probe goes in the thickest part of the flat without resistance (like a knife through butter). BTW: go in from the top not the side or all that wonderful juice will flow out!
You'll notice I made no mention of temps there...that's because temp is not the first but third in the priority of elements when smoking briskets with the first two being look and feel. Personally, when the color (that we like) is reached my temps are somewhere in the 145-160º range. Every brisket is/can be different, not to mention type of smoker and temps used. I know from past smokes approximately how long it will be before it finishes after wrapping and start probing it 1/2 hour early. I use a thermapen for the feel so by default the temp reading comes along for the ride. Finishing temps again vary (can't stress this enough, it's done when its done via the "feel") but their range seems to end up between 198-215º. Guess a good thumb would be 203º.
Good luck & Keep Smoking - it's get better!