Dude, stop using ZooTycoon for your husbandry guides. Learn the behaviors of the animals. Ask yourself questions like: "Why should these animals be mixed?" "What is the absolute worst that could happen?" And play out that scenario, because it will happen. "What message will this send to the visitors?" "Does it enrich the animal's lives?"
Thank you for sending out this clear, honest message! Trust me, @Macaw16: that's the best advice you could wish for. http://cdn.meme.am/instances/53355361.jpg
What animals (mostly primates please) can mix with white cheeked gibbons? Siamangs? Lion tailed macaques ( I know they are aggressive)? Langurs?