they do the task you assign them to, not sure where you get this from, if you don't assign them some automatically do something but if you assign them tasks its what they do, if you assign them to defense thats what they will always do, if you assign them to crops thats what they do, if you assign them to the scrap stations thats what they do and for the op, you need some people i think, i donk't think codsworth works on crops, i've never seen him do that and i tried assigning him to crops, you need about a dozen to 14 of each crop, you can do more but each settler accounts for 6 crops, so you need like 4 or 5 people assigned to crops to make sure all the plants are producing, i usually have 14 of each, corn,mutfruit, tato then 10 carrots, 2 razorgrain, 2 of each kind of melons and thats my standard "loadout" for the castle and sanctuary and that assures i have enough for adhesive and overall food for the settlers, smaller settlements need less but if you want adhesive just plant a dozen to 15 of each, mutfruit, corn and tato, you'll need settlers to work on them and thats it, do that for each settlement and you'll have plenty of adehsive, you'll have hundreds and hundreds before you know it. but you need water also, so build industrial purifiers, i have 8 purifiers at the castle and 8 at sanctuary. and thats lots of water, hundreds of bottles every day.