There is a certification available for agents through IBCCES that trains agents in assisting clients with autism and special needs. You can check their website for a list of certified agents. Of course, that doesn't guarantee the agent has personal experience, but it is one more level of training that you could look for. you might want to try asking around on Message boards dedicated to the special needs community to see if anyone there has an agent they have worked with that did a good job. As an agent, I know about the programs for autistic and special needs families, but I don't have direct experience using those programs. if you want someone who knows it on a personal level, you'll definitely have to do some interviewing or get referrals from other families that have similar needs.
The world is becoming much more in tune with special needs travelers, I'm sure you will be able to enjoy a wonderful vacation on Royal with your family!