Spam feeding carrots. Do it manually by highlighting him then right-clicking the carrots in your inventory.
+Moral food has no effect once they go into food boxes. -Moral too, for that matter. All food, once placed inside the food box only contribute their food value, not water or moral or any other effects. You are effectively "feeding" the food box to increase its food value, and other NPCs (or you) can "eat" from the food box later, drawing on its food value. There is no record of whatever items going into it.
Rain collector is broken and don't work for NPCs. I tried spamming the whole work area with them and they don't work either. The glowing blue circle is a big fat lie. Use a well. If you can't scrounge out the iron ingots needed for the well then you can manually give them water using water skins or bowls, to tide things over until you can craft a well.
To initiate sex between a PC and NPC, you need a positive relationship of at least 51 between that PC and that NPC. There must also be a H-animation enabled for that interaction. AFAIK none of the Yona x (normal/variant) Young Man scenes have been implemented in-game yet, so you can't initiate consensual sex between Yona and a grown-up son of the MC. (DLC sons might be a different story, I think?)
To check, click the NPC while controlling Yona and see if there's a sex option under Talk. If the NPC responds with "not yet" (or rarely "..."), then there is a H-scene and you just need to get their relationship to 51 and above. If Sex isn't even an option then there is no consensual H-scene implemented yet.
Click to highlight the NPC, click status from the pop-up options, click the "Order" tab on the NPC's status menu, then click
on "Allow love" under comunication (sic) and make sure it is disabled.
Actually, come to think of it, do that for every NPC and don't ever bother with the hot mess that is the relationship system. Unless your colony devolving into spontaneous Rimworld-style chaos is your thing. As a bonus, you now don't have to bother with stupid buggy houses either.
Just enable them back selectively for NPC you WANT inter-NPC relationships to happen (either positive or negative), after screening for personality types.
They will still get horny, but IIRC it shouldn't be a problem with Allow Love disabled. You can still lower lust using the human toilet (staff it with a random female captive, you don't even need to befriend them first), and for Life Orb farming purposes it's in fact even easier with Allow Love disabled because they have lower thresholds for using the toilet with Allow Love turned off. (And I think they get +1 moral from it too)
Stuff crafting mats into storages (cloth/spider/wing). Stuff inside them area available for crafting from nearby workbenches. Regularly top them up with a fat surplus so you don't have to go hunt down mats later. If needed, exploit the pause functionality to place storages/workbenches closer than they are normally allowed. (Just not too close to the point you have problems ctrl-clicking them.)
Put misc. stuff into a chest (or central collection of chests) in a dedicated spot so you know where to go look for items you couldn't find a use for previously.