Ok, calculate how many veg & spuds you need to feed the male teenagers and selves, then double the quantity to cook with the roast. When the veg come out of the oven, put the extras in a separate pot with a sticky note with the skull and crossbones drawn on it, which is the signal that if said teenagers eat them, then there will be Blood For Breakfast. Their Blood. Works most of the time. The skull & crossbones sticky note is very effective, except for chocolate cake.