Maybe a reasonable PvP option that still kinda fits the atmosphere would be to have a food fight sorta thing. Like the food fight equivalent to paintball. Once the hearthlings health bar is covered with food they’re “knocked out” of the competition. Different foods could have effects like a knockdown (watermelon/pumpkin) or a DoT (golden gourd curry lol), advanced food effects granted from higher level cooked foods or foods specially treated by different crafters (engineers). The winning group would get a morale boost and the others a penalty. Nobody would have to worry about their hearthlings getting killed, it’d all be in good fun, and the penalty wouldn’t be as severe as say losing a war with kobolds (unless players got too reckless with their food supplies). This would keep players on friendlier terms early game as food is such a vital resource to sustain and grow your population. Especially aggressive players will find themselves struggling to maintain their towns and lagging behind in growth, giving the other players a chance to get ahead. Encouraging players to keep up with combat, farming, and crafting instead of just trying to take everyone out with just combat. Late game perhaps the food covering the hearthlings health bars keeps the owner from seeing their health for a period of time (making combat a gamble), maybe the food attracts bugs requiring the herbalist’s help to prevent sickness/disease, or pests in the area with the most affected food soaked hearthlings needing a Trappers attention or they’ll occasionally startle your hearthlings.
While I definitely think hearthlings killing other hearthlings goes against their very nature, a friendly food fight can’t hurt right?