Give your smoker to the one with the "BA". They may very well leave it in the backyard for you to use & smoke good "Q" for them. The one with the "BS", build an UDS for them. The one graduating from high school, have that one "Help" you build the UDS. Once the UDS is done, claim it is too valuable to move & keep that in the backyard as well. Then make the best smoked meal you have ever made in your life & Thank God your house is almost empty.
On a more serious note, you have been a great Dad to them, so whatever you can provide is what they will accept. Just make sure it is from the heart if it can't come from your pocket. Adults know when times are hard. Good kids know as well. To me, it seems you're a good husband & father & that emotion will come through with whatever you present to your children for their graduation. Good luck.