Although I like the idea of the pets being mangy, decrepid and quite mad. But that seems too much of a disadvantage to compensate it with them requiring less pasture. Once you are in the first cavern, you have plenty of pasture unless you have 20 cows, at which point you just flood more cavern, and get moss growing.
I think the food/leather based domestic creatures should be diseased, but they should have access to evil creatures. For example they should have poor food capabilities from all their creatures, but should have access to Giant Cave Spider Hatchlings ("GCS hatchlings" for short when listed), they have the same venom, but are easy to kill, but reproduce quickly. Think of a nest box being for a wild GCS, and when the hatchlings get too big they kill their captors are released.
Trolls can be kept, but they need to be diversified. Multiple types, upgradeable to. E.g. Troll (basic, wrestler), Club Troll (blunt damage), Spear Troll (Piercing attacks), Axe Troll (No more limbs for you). Armour could also be added, but it should be minimal, think plates of metal strapped to them using rope.
I think goblins should have an increased learning rate in more sadistic weapons e.g. knives, lashes, whips, fist-weapons. Making trolls more useful as pure killing machines.
Goblins should have a high breeding rate (A bit lower than kobolds), and quick maturity (2 years). They should use numbers to their advantage, but as you know they are individually weak.