sims being autonomously mean to each other

My sims are continuously choosing mean dialogue options when chatting to their close friends and family members. Giving one of my sims the loyal trait seemed to stop the problem for him but despite a previously full friendship bar and nothing but good sentiments towards each other his brother continues to say mean things to him. It is not just these two that were affected and none of my sims have negative traits that would prompt them to say these things. 

I play on xbox with no CC or even cheats applied.