I respectfully disagree. The signs on the companion restroom do not have a family symbol. This is not the symbol on the companion restrooms.
http://www.exitsignwarehouse.com/product/ESW-ADA-F.html
They have a wheel chair symbol and a male and female symbol.
Since Disney lists these restrooms in the guide for disabilites, I think there intent is clear. Although I do know many people prefer to use them just because it is "easier" for them personally. (Not directed at anyone, just in general)
To quote Sue the Disabilities Moderator:
"For some people, the Companion Restrooms are the only 4-6 toilets in the park that they are able to use.
So, speaking for people who have no other choice, I only ask that people think of what options they might have besides using the Companion Restrooms. If there are other options you can use, we would appreciate if you would choose another option and leave the Companion Restrooms for the people who have no other choices and can only use those 4-6 toilets."